Section SCHIZODONΤΑ

Superfamily PTERIACEA

Triangular, with straight margins and acute summit; compressed; substance highly polished and silvery; valves with longitudinal radii on more than half the disc, about thirteen in number; anterior side with rugose, obtuse, oblique, finer and more approximate lines. Length 234. Rare.

Family PINNIDAE

Genus ATRINA Gray

1840. Atrina J. E. Gray, Synopsis of the contents of the British Museum, p. 151, nomina nuda.

1842. Atrina J. E. Gray, idem, p. 83.

Type: Pinna nigra Chemnitz. (Recent in the Indo: Pacific.)

Gray characterized the genus in 1842 as follows:

The Pinna have an elongated shell with a longitudinal crack filled with a cartilage in the middle of each valve, and Atrina are shorter shells without any such crack.

Shell thin, fragile, equivalve, gaping posteriorly, cuneate. Umbones sharp, pointed, terminal, anterior. Ligament lodged in a long narrow groove. Hinge edentulous. Byssal notch small, situated beneath the umbones.

Atrina is separated from Pinna, to which it has been frequently assigned as a subgenus, by the absence of the medial longitudinal sulcation. It is confined to the warmer waters and is never abundantly represented.

The genus apparently began as early as the late Paleozoic. The Recent species bury themselves in the sand and mud along tropical and subtropical shores. Only a single species has been reported from the Alum Bluff, but this ranges with some variation through both the Chipola and the Oak Grove. Fragments of an indeterminate form occur also in the Shoal River.

Atrina chipolana Dall

1898. Atrina (argentea var. ?) chipolana Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 662.

Dall describes this species as follows:

This form is only represented by fragments. It would appear to attain about the size of A. argentea, but to be somewhat more convex and arcuate. The chief distinction is in the sculpture; the dorsal areas of the valves of both have about five equidistant radial riblets; the ventral areas in argentea have a few radial ribs near the middle of the valve, below which the sculpture becomes obsolete; in chipolana the ventral areas are sculptured with distinct oblique, concentric waves, with about equal interspaces; the upper ends of these waves terminate abruptly where they meet the longitudinal riblets, so that the sculpture of the ventral is strongly contrasted with that of the dorsal areas. This form also appears to increase in width more rapidly than the argentea. On the whole, the two appear specifically distinct, but a complete description must be deferred untił better material enables the characters to be fully elucidated.

Type: U. S. Nat. Mus. No. 114778.

Type locality: No. 2213, 1 mile below Baileys Ferry, Chipola River, Calhoun County, Fla.

Conrad's original description of Atrina argentea is as follows: 16

There are no fragments worth figuring, and the original description can not be amplified from any material furnished by the later collections. It is possible that there may be more than an individual variation between the Oak Grove and the Chipola forms, as the Oak Grove fragments seem to indicate a broader, less convex species.

Occurrence: Chipola formation, locality 2213P. Oak Grove sand, locality 2646P.

Family PEDALIONIDAE

Genus PEDALION (Solander MSS.) Huddesford

1770. Pedalion Huddesford, Duo indices ad synopsin methodicam conchyliorum Martini Lister, Index II, p. 23.

= Melina Retzius, 1788.

=Perna Lamarck, 1799.

Type: Ostrea isognomum Linnaeus. (Recent in the East Indies.)

Shell without well-defined auricles, subquadrangular to subcuneate, compressed. Exterior surface lamellar. Interior nacreous. Umbones sharp, anterior, terminal. Hinge edentulous. Area wide, furnished with a series of elongated cartilage pits set normal to the margin. Pallial line simple. Muscular impression large, slightly eccentric.

The genus is sparsely represented in the Mesozoic and Cenozoic faunas.

The reported occurrence at Oak Grove is the only record of the presence of this genus in the Alum Bluff.

Pedalion solereperta (Maury)

1910. Perna solereperta Maury, Bull. Am. Paleontology, vol.

4, No. 21, p. 33, pl. 8, fig. 8.

Maury describes this species as follows:

Shell very inequilateral, small, compressed, with the general outline of P. ephippium Linnaeus. Unfortunately the only valve found is broken, but the portion of the cardinal area that remains shows distinctly two of the series of cartilage pits. Exterior of the shell with numerous fine radiating riblets not appearing over the earlier 5 millimeters of the shell.

Length of shell 12, width 8 millimeters.

This appears to be the first true Perna found in the Florida Tertiaries.

Oak Grove, Santa Rosa [now Okaloosa] County, Fla.
Cornell University collection.

Both the description and the figure are inadequate, but there is nothing to supplement them in any of the later collections.

Occurrence: Oak Grove sand (Cornell University). Family PTERIIDAE

Genus PTERIA Scopoli

1777. Pteria Scopoli, Introductio ad historiam naturalem, p. 397.

Type: Mytilus hirundo Linnaeus. (Recent off the coast of England and southward through the Mediterranean.)

Shell inequivalve, inequilateral, auriculate. Anterior ear comparatively small, posterior aliform. Byssal sinus under anterior auricle of right valve. Exterior surface almost smooth, lamellar or striated. Interior nacreous. Umbones low but sharp. Hinge line elongated, straight. A single cardinal tooth placed under the umbone of each valve, commonly supplemented by a laminar lateral tooth. Ligament marginal, partly internal, partly external. Pallial line entire. Adductor impression subcentral.

The genus has a vast stratigraphic range from the Silurian onward. The Recent species number about 120 and live chiefly in tropical and subtropical waters. Among them may be mentioned the Antillean pearl oyster, Pteria radiata Leach.

The picturesque name of the type species was doubtless suggested by the outline of the shell, which is not unlike that of a swallow on the wing.

Only a single species has been found sufficiently well preserved to receive a name, and even this occurs in so fragmentary a state that it has not been figured. Aside from P. chipolana, which is apparently quite common at the single horizon at which it occurs, there is another rather closely related Chipola species and also an Oak Grove form of the group of the P. multangula H. C. Lea from the Chesapeake Miocene. No trace of the genus has been observed in the Shoal River material.

Pteria chipolana Dall

1898. Pteria (argentea var.?) chipolana Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 669.

Dall describes this species as follows:

Small, with a straight hinge line and narrow, deep ligamentary sulcus, the right valve with a small, well-marked cardinal tooth fitting into a small pit in the opposite valve; anterior wing short, small, with a narrow byssal sinus marked on the auricle by a short groove, external surface smooth, the posterior wing feebly set off; valves rather compressed, none of the valves exceeding 25 millimeters in length.

It is probable that this represents a species distinct from that of Vicksburg, but the material in my possession is insufficient to determine the question, but the type of P. argentea shows little trace of a byssal sinus and is more inequilateral than our shell.

Type: U. S. Nat. Mus. No. 114881. Type locality: No. 2213, 1 mile below Baileys Ferry, Chipola River, Calhoun County, Fla.

and crowded with laminae sinuated by the shallow byssus, the posterior auricle relatively large and quite well defined. The entire known surface with the exception of the anterior auricle is microscopically crackled and chased with regularly disposed incised lines. The surface is mottled with a reddish brown, which seems to be a remnant of the original color pattern. The ligament sulcus is very shallow and the cardinal tooth rude.

Fragments of a third species occur in the Oak Grove beds. This form was apparently much thicker and heavier and had a shell structure similar to that of P. multangula H. C. Lea. The nacre is pearl-gray and highly iridescent, as in the Miocene species, and there are traces of similar undulatory growth lines and radiating threadlets. The ligament area is wide and the armature well developed for the group.

Occurrence: Chipola formation, localities 2213, 2564°, 3419г, 2211P.

Superfamily OSTRACEA
Family OSTREIDAE

Genus OSTREA (Linnaeus) Lamarck

1758. Linnaeus, Systema naturae, 10th ed., p. 696. 1799. Lamarck, Prodrome d'une nouvelle classification des

coquilles: Soc. hist. nat. Paris Mém., p. 81.

Type: Ostrea edulis Linnaeus. (Recent off the European shores from Iceland to the Adriatic.)

Ostrea, the common oyster, is doubtless by reason of its great economic value the most widely known of the molluscan genera. The shell is inequivalve, generally irregular and more or less inequilateral. Except in the larval stages it is attached by the convex left valve. The right valve, which is flattened or slightly concave, serves as a cover. The hinge is edentulous. There is a single muscle scar, the posterior, and this is subcentral. The pallial line is simple but not well defined.

The genus has been prominent in all the molluscan faunas from the Mesozoic onward. Two hundred and forty species have been recognized in the Cretaceous alone, and throughout the Tertiary Osirea forms one of the most conspicuous elements of nearly every fauna. Nevertheless, the later Tertiary species are of little value as horizon markers because of their wide stratigraphic range. As in all attached forms the limits of variation are wide.

apparently restricted to the Oak Grove, whereas 0. trigonalis, O. podagrina, and the prolific O. normalis Dall (O. mauricensis of authors) are restricted in the Alum Bluff section to that portion formerly known as the "Hawthorn beds." There is no conspicuous development of the genus at any horizon, and during the Shoal River epoch conditions must have been decidedly unfavorable.

Adult shell rarely exceeding 7 centimeters in altitude; radial sculpture strongly developed on the left valve:

Radials on the left valve rarely exceeding 15 in number,
regularly imbricated by the incrementals.

Ostrea pauciplicata Dall.
Radials on the left valve usually exceeding 15 in number;
concentric sculpture usually feeble and irregular.
Ostrea rugifera Dall.

Adult shell generally exceeding 7 centimeters in altitude:
Left valve strongly plicated radially:

Shell rather thin Ostrea haitensis Sowerby.
Shell very heavy
Ostrea podagrina Dall.
Left valve nonplicate or feebly and irregularly undulated:
Outline broadly ovate, irregularly plicate, as a rule;
ligament area usually low, broad, and flattened.

Ostrea trigonalis Conrad. Outline narrowly ovate, usually elongated, not radially plicate; ligament area usually high, narrow, and medially excavated Ostrea normalis Dall.

Ostrea pauciplicata Dall

Plate X, Figures 3-4

1898. Ostrea sellaeformis var. pauciplicata Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 678.

Dall says:

Shell fan-shaped with acute beaks, thin, with few (7 to 15) rather large, loosely imbricated radial but not divaricating ribs, the scales more or less fluted, thin, and elevated; upper valve falcate, with concentric laminae; structure flattish and thin.

Dimensions: Right valve, altitude, 47.0 millimeters; latitude, 28.0 millimeters. Left valve of another individual, altitude, 55.0 millimeters; latitude, 37.0 millimeters.

The form is apparently peculiar to the Oak Grove horizon.

Occurrence: Oak Grove sand, localities 2646a, 5632°, 5630P, 7054°, 9961°.

Ostrea rugifera Dall Plate X, Figures 1-2

1898. Ostrea sellaeformis var. rugifera Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 678.

Dall describes this species as follows:

Shell rather thin, irregular, coarsely ribbed, more or less imbricated, margin plicate, form tending to ovate or rounded.

Dimensions: Right valve, altitude, 61.5 millimeters; latitude, 37.0 millimeters. Left valve of another individual, altitude, 58.0 millimeters; latitude, 38.0 millimeters.

Cotypes: Right valve, U. S. Nat. Mus. No. 114570; left valve, U. S. Nat. Mus. No. 114571.

Type locality: No. 2211, lower bed, Alum Bluff, Liberty County, Fla.

Shell rather small, rudely ovate or ovate-trigonal in outline, the lower valve slightly convex and overreaching the flattened upper valve along all but the dorsal margins. External surface of left valve normally sculptured with 20 to 25 cordate riblets which show a slight tendency to diastomose but are for the most part continuous from the umbones to the ventral margins. Concentric sculpture manifested in irregular nodulations of the costae and more rarely in imbricating lamellae. Surface of right valve sculptured with very thin, closely appressed, concentric lamellae, about 30 in number in perfect individuals. Ligament area short and narrow, usually a little twisted; hinge edentulous. Submargins finely punctate or dentate. Single muscle scar pyriform in outline in fresh individuals, posterior in position, a little below the median horizontal. Inner margin of left valve finely crenulated.

Ostrea rugifera Dall is most abundantly developed at Alum Bluff and is consistently more regular in out

Okaloosa County, Fla.

The right valve as well as the left is usually quite strongly falcate. Radial sculpture is absent upon the upper valve. The external surface of the lower valve is very prettily frilled by the free-edged and unusually regular concentric laminae. The beaks are compressed, the ligament area is narrow and trigonal, and the medial depression is deep. The submargins are commonly punctate or minutely nodulated, and the single muscle scar is pyriform and rather high.

The species is well characterized by its thin shell, falcate outline, fanlike radials, and uniform concentric lamination. It is more coarsely sculptured than O. rugifera and more regularly sculptured than O. haitensis. It seems to be sufficiently distinct from O. sellaeformis to deserve generic rank.

locality than it is along the Chipola. The Chipola River individuals are elongated and are as a rule more sparsely ribbed and more conspicuously laminated. Some of the end members are separable with difficulty from O. pauciplicata of the Oak Grove. The radials of O. pauciplicata are, however, more undulatory, usually broader, and less numerous and the concentric laminae more regularly fluted.

Occurrence: Chipola formation, localities, 2212a, 2213a, 2564, 3419, 9994 P, 2211 pr, 2568г, 7183°, 3424P 7468°, 49765, 4977, 4986P.

Ostrea trigonalis Conrad

1829. Ostrea sp., Lesueur, Walnut Hills fossils, pl. 4, fig. 17; 1855. Ostrea trigonalis Conrad, Acad. Nat. Sci. Philadelphia

Proc., vol. 7, p. 259.

1898. Ostrea trigonalis Conrad. Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 681.

1904. Ostrea trigonalis Conrad. Glenn, Maryland Geol. Survey,

Miocene, p. 381, pl. 101, figs. la, lb.

1909. Ostrea trigonalis Conrad. Grabau and Shimer, North American index fossils, vol. 1, p. 465, figs. 621, a, b. (After Glenn.)

Conrad described this species in 1855 as follows: Triangular, flat, surface irregular, with some indistinct radiating lines; muscular impression obliquely suboval, situated nearer the summit than the base; margin somewhat ascending, submargin carinated. A single imperfect upper valve is all that I have seen of this shell but it is widely different from any other Eocene species known to me.

Type locality: Jackson, Miss.

A few of the excellent plates of Lesueur, a French engraver, were distributed privately but never properly published, so that his name would have no standing even if he had given one.

Ostrea trigonalis Conrad is heavy, commonly irregular, and varies widely in outline. The umbones are generally subcentral and fairly straight, the hinge area rather broad and flat, with a shallow central channel. The strong vermicular sculpturing of the submargins in front of the hinge area, particularly in the right valve, forms one of the best diagnostics of the species. The outer surface of the heavy upper valve is coarsely wrinkled, that of the lower valve in some specimens is smooth, in others sculptured with

This species appears to be related to O. imbricata Lamarck; it differs, however, in its general form, which is oblong and not orbicular, and in the number of external radiating folds, which are only six or seven in our shell.

Type locality: Near San Jago, Santo Domingo, West Indies.

Shell large, commonly 10 or 12 centimeters across, solid but not greatly thickened. Both valves flattened and subcircular to broadly ovate in outline, the left a little more convex as a rule than the right and a little broader. Left valve strongly plicate, the right variable, in some individuals similar in sculpture to the left, in others almost smooth; plications taking the form of sharp, V-shaped ridges, generally six or seven in number upon the medial portion of the disk, originating at the umbones and growing increasingly prominent toward the ventral margin; two to four finer costals usually developed near the dorsal margins and fortuitous secondaries introduced near the ventral margin, either intercalated between the primaries or diastomosing from them. Concentric laminae overriding the costals and commonly subspinose upon their crests. Ligament area varying from high and rather narrow to low and broad but generally small and rather flattened submargins, in many specimens finely corrugated. Single muscle scar large, transversely elliptical to subcircular, slightly posterior to ventral in position. Margins simple in the heavy shells, more or less fluted in the lighter.

Ostrea haitensis Sowerby is characterized by its

The muscle scar is semioval, and in many specimens deeply impressed.

The species has been reported from the fuller's earth beds at Rock Bluff and from Sopchoppy. It is a poorly characterized form, not sufficiently well preserved to be identified with assurance.

It is quite possible that the few valves in question may be more properly referable to the less ponderous Ostrea haitensis Sowerby.

Occurrence: Chipola formation, localities ?2566", ?7468, 6175′, ?67695, ?6209г.

Ostrea haitensis Sowerby

1850. Ostrea haitensis Sowerby, Quart. Jour. Geol. Soc. London, vol. 6, p. 53.

1873. Ostrea haytensis Sowerby. Gabb, Am. Philos. Soc. Trans., vol. 15, p. 257.

1866. Ostrea virginica Guppy, Quart. Jour. Geol. Soc. London,

vol. 22, pp. 576, 577.

Not Ostrea virginica Gmelin, 1792.

1898. Ostrea haitensis Sowerby. Dall, Wagner Free Inst. Sci.

Trans., vol. 3, pt. 4, p. 685 (part).

1917. Ostrea haitensis Sowerby. Maury, Bull. Am. Paleontology, vol. 5, No. 29, p. 182, pl. 31, figs. 1, 2. Sowerby described this species in 1850 as follows: Testa oblonga, crassa, plicata, plicis paucis (senis ad septenis), magnis, undulatis, subsquamosis, squamis nonnunquam subtubulosis; limbo interno omnino glabro.

and, for an oyster, quite regular radial plications. The young are separated from O. rugifera of the same size by the coarser ribbing in the right valve and the less closely appressed lamellae in the left. O. pauciplicata is more falcate and more regularly laminated concentrically.

Occurrence: Chipola formation, localities 10611°, 10609°, 10610P, 2212°, 2213a, 2564P, 3419P, 9994г, 6775P. Oak Grove sand, localities 2646pr, 5630P, 70548. Shoal River formation, localities 3742P, 5618P, 10612г.

Ostrea podagrina Dall Plate X, Figures 5-6

1896. Ostrea podagrina Dall, U. S. Nat. Mus. Proc., vol. 18, p. 22. 1898. Ostrea podagrina Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 682, pl. 30, figs. 5, 6.

Dall described this species in 1896 as follows:

Shell compact, thick and heavy, wider than high, with very short wide beaks, coarsely imbricated surface, inflated shell, with three or four strong, wide, rather irregular radial plications; interior smooth, distinctly marginated, with a large subcentral adductor scar; hinge and beak flat, the ligamentary area in the flat valve hardly excavated, the edges of the flat valve near the cardinal border with two obscurely wrinkled projecting crura, which fit into shallow depressions in the opposite valve; elsewhere there are no striae or pustules on the edge of the valves. Height, 110; width, 100; diameter, 50 millimeters.

Type: U. S. Nat. Mus. No. 135127. Type locality: No. 2612, west bank Suwannee River near Sulphur Springs Station, Lafayette County,

Fla.

dant species in Cumberland County, N. J., the environs of Gabb's type locality, is O. percrassa Conrad, a species characterized by just such a hinge as that exhibited by O. mauricensis. Although it is difficult to prove anything by a young oyster, yet the chances are favorable that Gabb's type is the young of the species abundant in that vicinity rather than

Ostrea normalis Dall

Plate XI, Figures 3-4

1898. Ostrea georgiana, forma normalis Dall, Wagner Free Inst.

the adult state from the area north of Hatteras and which probably does not occur north of Georgia. Furthermore, the contour, habit of growth, and general hinge characters are strikingly similar to those of O. georgiana of the earlier Tertiary of the Gulf region,

Sci. Trans., vol. 3, pt. 4, p. 684.

p. 123.

Not Ostrea mauricensis Gabb, 1860.

Dall described this species in 1898 as follows:

The typical O. georgiana are the enormous senile specimens with shells ranging to 2 feet long and 3 or 4 inches thick. The young and really more normal specimens have been overlooked, though much more abundant, or referred to other species, chiefly O. virginica, from which they differ by their more elongated, usually straight, deeply excavated cardinal area and the absence of ribbing on the lower valve in most specimens.

Dimensions: Right valve, altitude, 95.0 millimeters; latitude, 55.0 millimeters. Left valve of another individual, altitude, 100.0 millimeters; latitude, 50.0 millimeters.

Cotypes: U. S. Nat. Mus. No. 153848. Type locality: No. 323, Devil's Mill Hopper near Hawthorn, Arredonda County, Fla.

Shell solid, usually thick, elongated ovate-trigonal in outline, sometimes very narrow and rudely cylindrical. Right valve flattened. Left valve feebly convex. Umbones narrow and compressed, erect or slightly inclined. Component concentric layers usually visible both on the disk and along the lateral margin, most expanded, as a rule, a little more than half way down from the dorsal to the ventral margin, thus giving to the exterior a pseudoconvexity which the interior does not possess; concentric laminae probably frilled much as in O. compressirostra Say but with the free edges usually broken away. Ligament area usually high and narrow, strongly depressed medially in the left valve, conspicuously elevated in the right, especially toward its ventral extremity. Lateral margins well differentiated both by the change in the plane of the hinge and in the direction of the incrementals; vermicular sculpture rarely developed upon the submargins. Single muscle scar semielliptical, deeply excavated in the heavier individuals, slightly posterior and ventral in position.

Ostrea mauricensis Gabb, the species to which these forms have been commonly assigned, was described from a shell 111⁄2 inches long from New Jersey. The outline is similar to that of many of the individuals from Florida, but unlike the vast majority of them the ligament area is low, broad, and flattened. The abun

The

the forms. They have been kept apart, however, because they are so readily separable and because of the difference in stratigraphic occurrence. species is very abundant at many localities in northwest and central Florida, notably in Leon, Levy, and Alachua counties. It is restricted, apparently, to those beds formerly grouped under the name of the "Hawthorn formation" and now considered as Alum Bluff, and to the so-called "Grand Gulf beds" overlying the Alum Bluff in the type section.

Occurrence: Chipola formation ("Hawthorn beds"), localities 2566P, 3415, 2302, 6175P, 6769°, 6776, 6778г, 2324P, 6783, 361, 5P, 322P, 6801P, 323, 369pr, 365a, 356a, 21165, 5629P.

ISODONTA

Superfamily PECTINACEA

Family PECTINIDAE
Genus PECTEN Müller

1776. Pecten Müller, Zoologiae danicae, prodromus seu animalium, p. 248.

Type: Ostrea maxima Linnaeus. (Recent off the coast of Europe from Norway to the Straits of Gibraltar).

Shell approximately equilateral, inequivalve, usually suborbicular, auriculate; right valve, as a rule, the more convex, not adherent but attached by a byssus. Hinge line straight. Resilium central, internal, triangular. Interlocking grooves and ridges diverging from the apex of the resilial pit. Pallial line simple. Monomyarian; adductor impression rounded, posterior.

The earliest true Pecten known is from the Cretaceous. The Recent species number more than 200, and their distribution is world-wide.

Pecten does not constitute the conspicuous element in most of the Alum Bluff faunas that it does in many of the formations of the later Tertiary. The abundance of the large Chlamys (Lyropecten) sayanus gives to the Oak Grove fauna the general aspect of that of the Chesapeake, and the Chipola faunas represented in the "Sopchoppy limestone" and in the fuller's earth beds at Quincy have much the same general make-up. In