from 90°. Anterior dorsal margin feebly convex, much more produced than the obliquely truncate posterior slope. Basal margin asymmetrically arcuate, more strongly upcurved behind than in front. Lunule not sharply delimited, indicated by the flattening of the shell. Escutcheon narrow, elongate, cordate, flattened but not depressed. A subcutaneous radial sculpture developed, usually obsolete in the umbonal region but fine and regular toward the base, where the sulci number about 12 to the millimeter and are separated by flat interradials that are more than double their own width. Basal margin finely serrate in harmony with the radials. Concentric sculpture restricted to grayish color bandings and obscure resting stages. Ligament entirely internal, lodged in a small cuneiform resilium rudely parallel to the anterior dorsal margin. Hinge rather delicate. Teeth taxodont, arranged in two discrete series, the posterior including six in the type, the anterior three times as many. The half dozen umbonal teeth in the anterior series exceedingly small and crowded, the medial teeth in both the anterior and posterior series slender but well elevated. Muscle impressions and pallial line very obscure because of the thinness of the shell. Dimensions: Altitude, 3.2 millimeters; latitude, 4.0 millimeters; semidiameter, 1.2 millimeters.

Type: U. S. Nat. Mus. No. 352288.

Type locality: No. 3742, Shell Bluff, Shoal River, Walton County, Fla.

The Shoal River species is larger than that from the

Chipola and relatively higher. The radial sculpture is commonly a little stronger and more persistent in the umbonal region, but this is not a constant character.

Occurrence: Shoal River formation, localities 3856P, 2645P, 3742°, 10658′, 2238P, 9957г.

Nucula sinaria Dall Plate II, Figure 4

Type: U. S. Nat. Mus. No. 135820. Type locality: No. 2646, Oak Grove, Yellow River, Okaloosa County, Fla.

Nucula sinaria Dall exhibits a remarkable range of variation in dimensions and relative proportions. The type is larger, much higher, and more trigonal than the average individual from Oak Grove. The differences in the peripheral members are sufficiently great to be given subspecific rank, but as they are apparently of no stratigraphic or geographic significance there is little to be gained by splitting the series. The depressed escutcheon is a character shared by only one other Alum Bluff species, Nucula dasa, from the Chipola formation on Choctawhatchee River. The Chipola species is usually lower and heavier than N. sinaria and is more inflated in the umbonal region. Occurrence: Oak Grove sand, localities 2646 pr, 5632a, 5631°, 5633°, 7054°, 9961°, 10659°.

Nucula dasa Gardner n. sp. Plate II, Figures 5-7

Shell highly polished, small, heavy, quite strongly inflated. Umbones quite prominent, obtuse, flattened upon their summits, opisthogyrate, set well within the posterior third. Umbonal angle not far from 90°. Posterior dorsal slope very steep. Anterior rather gentle and feebly arcuate. Basal margin more sharply upcurved in front than behind. Lunule narrow, elongated, not sharply delimited but defined by the flattening of the shell and by the darker coloring of the lunular area. Escutcheon rather narrow, cordate, feebly depressed, the depression emphasized by the slightly raised margins. Radial sculpture restricted to exceedingly fine lines, least faint near the base but commonly obscured even there by the surface glaze. Basal margin finely but sharply serrate. Concentric striae also very faint. Resting stages rarely developed. Ligament internal, lodged in a very small cuneiform resilium elongated parallel to the anterior dorsal margin. Hinge dentition strong and heavy. Teeth

Dall describes this species as follows:

Shell small, solid, trigonal, polished, with fine radial striae, more distinct near the basal margins, and faint, concentric, rather irregular furrows, obsolete over most of the valve but tending to be stronger near the anterior and posterior slopes; here and there one crosses the whole shell like the indication of a resting stage; dorsal slopes nearly straight, base arcuate, ends rounded; lunule absent, escutcheon impressed; striated, the margins not pouting in the middle; beaks prominent, obtuse; interior brilliantly pearly, muscular impressions deep; the basal margin finely crenulate; hinge strong, wide; the chondrophore oblique, heavy; anterior teeth wide, strong, about seventeen, posterior about seven. Longitude of shell, 4.75 millimeters; altitude, 4 millimeters; diameter, 2.5 millimeters.

This species differs from the preceding (Nucula chipolana Dall) by its more trigonal, heavy, and pearly shell, its wider and proportionately heavier hinge, and its impressed instead of merely flattened escutcheon.

series in the type including 15, the posterior 7, the half dozen nearest the umbones in the anterior series very fine and crowded, the posterior teeth and, more especially, the anterior teeth away from the umbones, elevated, compressed, curved slightly toward the dorsal margins but not hooked. Muscle impression and pallial line usually very obscure because of the highly polished inner surface. Anterior scar placed well down toward the base at the distal extremity of the hinge, larger, less rounded, and more ventral in position than the posterior scar. Pallial line simple, moderately near to the basal margin.

Dimensions: Altitude, 3.2 millimeters; latitude, 3.55 millimeters; semidiameter, 1.5 millimeters.

Type: U. S. Nat. Mus. No. 352289.

Type locality: No. 7893, Boynton Landing, Choctawhatchee River, Washington County, Fla.

Nucula dasa Gardner, n. sp., is the heaviest and most inflated species known from the Alum Bluff. In these characters it is contrasted sharply with the coexistent N. chipolana Dall, which is the thinnest and the most compressed. N. dasa shares with N. sinaria the sunken escutcheon, but the shell is less inflated in the Oak Grove species and the umbones less prominent. Nucula dasa is known only from the type locality. Occurrence: Chipola formation, locality 7893г.

Nucula defuniak Gardner, n. sp.

Plate II, Figures 8-10

Shell of moderate dimensions for the group, not very strongly inflated in the umbonal region and compressed toward the ventral margins, rounded, trigonal in outline. Umbonal angle obtuse, not quite 90°. Umbones very small, opisthogyrate, posterior in position. Posterior dorsal slope consequently steeper than the anterior. Ventral margin asymmetrically arcuate, more strongly upcurved behind than in front. Lunule not defined, indicated by the flattening of the valves over a lenticular area, a slight darkening of the shell, and the closer radials. Escutcheon obscurely defined, cordate, flattened but not sunken, the shell substance darker as in the lunular area and the radials closer and stronger. Radial sculpture developed in the form of subcutaneous linear sulci, least faint toward the ventral margins, numbering 10 or 12 to the millimeter, and near the margin of the adult separated by flat interspaces of more than double their own width. Ventral margin finely crenate in harmony with the radials. Lunule sculptured with about 9 slightly wider radials separated by relatively narrow interspaces, the sculptured area cut off from the central portion of the shell and from the margin, which is microscopically serrated by the radials. Concentric sculpture restricted to an obscure color banding and a few ill-defined resting stages. Ligament internal, lodged in a narrow, cuneate, anteriorly directed resilium. Teeth arranged in two discrete series, 13 in number in the anterior series of the type, 7 in the posterior, the teeth shorter toward the umbones, especially in the anterior series, the medial teeth in each series very long and hooked, the hooks turned toward the dorsal margins. Muscle impressions placed at the extremities of the dental series, obscure, the anterior relatively higher and narrower than the posterior. Pallial line simple, distinct, distant from the basal margin. Inner margins in many specimens radially striate almost to the pallial line.

Dimensions: Altitude, 4.3 millimeters; latitude, 5.0 millimeters; semidiameter, 1.7 millimeters. Type: U. S. Nat. Mus. No. 352290.

Type locality: No. 5618, 31/1⁄2 miles southwest of De Funiak Springs, Walton County, Fla.

Nucula defuniak is very close to the type of N. sinaria in dimensions and outline but stands apart

from that species and from all the other Alum Bluff forms by reason of the radial sculpture upon the escutcheon.

The teeth in the anterior series of larger but less perfect individuals number as high as 18.

The species is best represented in the environs of its type locality.

Occurrence: Shoal River formation, localities 3856′, 5079, 9958г, 3748°, 3747°, 7261P, 7264P, 9960°, 9957г, 10603°, 5618°, 9959P.

Family LEDIDAE

Genus LEDA Schumacher

1817. Leda Schumacher, Essai d'un nouveau système des habitations des vers testacés, pp. 55, 172.

Type: Arca rostrata Gmelin==Leda pernula (Müller). (Recent in the North Atlantic.)

Shell solid, porcellaneous, transversely elongate, rounded anteriorly, more or less rostrate posteriorly; beaks proximate, commonly tumid, feebly opisthogyrate; exterior surface concentrically sculptured; hinge armature taxodont, the teeth arranged in an anterior and a posterior series; chondrophore subumbonal, trigonal; pallial line interrupted by a shallow sinus corresponding to the short siphons of the animal; inner ventral margins simple.

This genus also originated in the Paleozoic but in the Silurian, one period later than Nucula. The more than 80 living species have a wide geographic and bathymetric distribution, although the majority are boreal. Leda is conspicuously more abundant in the Miocene Floridian faunas than in those of the West Indies.

The smaller Alum Bluff Ledas, dissimilar as are the peripheral species, show an astonishing gradation, which relates even such unlike forms as Leda canonica Dall and Leda diphya Gardner, n. sp. The genus is abundant in the Chipola formation, being represented by eight species. In the Oak Grove sand Leda is remarkably rare. There is a single species peculiar to the formation and two other species, each of them represented by a single imperfect individual, one of which has been tentatively referred to a Chipola form and the other remains unnamed. A Shoal River Leda may be present at one locality. In the Shoal River formation the genus returns to prominence, though it is not quite so conspicuous at that horizon as it is in the Chipola. The three smaller Shoal River species are with one possible exception restricted in their range to the single horizon, though they have analogs in the Chipola faunas. The remarkable Leda basilissa Gardner, n. sp., recalls Leda pharcida Dall of the Wilcox fauna.

The relationship of the smaller Alum Bluff Ledas as indicated by the concentric sculpture may be expressed by the accompanying diagram.

Concentric sculpture close and flattened over the entire surface Leda? acuta Conrad. Concentric sculpture, if present, more or less elevated.

Leda proteracuta Gardner, n. sp., s. 1. Between 20 and 25 concentric ridges, most prominent medially, inclined to weaken and become obsolete laterally.

Leda proteracuta Gardner, n. sp., s. s. Between 15 and 20 concentric ridges, relatively coarse and distant toward the umbones.

Leda proteracuta dystakta Gardner, n. subsp. Concentric sculpture obsolete except near the tips of the umbones and the ventral margin.

Leda proteracuta leita Gardner, n. subsp. From 25 to 30 concentric ridges, as a rule, in many specimens irregularly spaced.

Leda proteracuta diamesa Gardner, n. subsp. Concentric ridges commonly acute, exceeding 30 in number in the adult:

From 30 to 40 acute concentric ridges.

Leda leptalea Gardner, n. sp. More than 40 obtuse or subacute concentric ridges---- Leda canonica Dall, s. 1. Concentric ridges exceedingly fine and closely crowded, 10 to 25 to the millimeter.... Leda canonica Dall, s. s.

Concentric ridges rarely exceeding 40 and rarely altogether obsolete upon the rostrum: Concentric sculpture persistent upon the rostrum Leda polychoa Gardner, n. sp., s. 1. Concentric sculpture more or less obsolete upon the rostrum.

Leda polychoa defuniak Gardner, n. subsp. Concentric ridges usually exceeding 40, altogether obsolete upon the rostrum.

Leda leiorhyncha Gardner, n. sp. Latitude of adult usually exceeding 7.0 millimeters; concentric sculpture conspicuously coarse and distant toward the umbones:

Concentric sculpture on the medial portion of the shell becoming abruptly finer and closer; escutcheon finely and regularly laminated.

Leda diphya Gardner, n. sp. Concentric sculpture uniform in character over the entire medial portion of the shell; escutcheon smooth or irregularly laminated--------Leda dodona Dall.

Leda basilissa Gardner, n. sp.

Plate II, Figures 11-12

Shell very large, exceedingly brittle, compressed, transversely elongated, slightly produced and rostrate posteriorly. Umbonal angle very wide. Anterior dorsal margin gently declining, posterior feebly conAnterior lateral margin smoothly rounded but not bowed beyond the distal extremity of the dorsal margin. Posterior extremity probably obliquely truncate. Base line arcuate, more strongly upcurved in front than behind. Umbones swollen near their tips, slightly overtopping the dorsal margins, the tips proximate and feebly opisthogyrate. Lunule sublinear, depressed, extending almost but not quite to the lateral extremity, outer margin sharply elevated. Escutcheon narrow, lanceolate, concave, unequally divided by a sharply elevated line that cuts off an inner lanceolate area. Incrementals of the inner area rudely parallel to the dorsal margin, of the outer area oblique to it. External surface finely and regularly sculptured concentrically, the sharply elevated, somewhat laminar threads of the umbonal area developing away from the umbones into crowded lamellae ventrally overlapping, raised slightly toward the anterior dorsal margin, abruptly disappearing at the edge of the lunule, bent abruptly outward and slightly downward at the keel, slightly flexuous across the keel, disappearing abruptly at the edge of the escutcheon; interspaces decidedly wider than the laminae upon the rostrum, not so wide upon the disk. Ligament internal, the pit wide, trigonal, sunk deep beneath the umbones. Dental series somewhat concavo-convex. The anterior series arched upward toward the dorsal margin, including 33 to 38 teeth, those at the extremities of the series short and straight, the medial teeth elevated and >-shaped, the apex of the angle directed toward the umbone. Number in posterior series probably a little higher. Adductor and pallial scars obscure.

Dimensions of left valve: Altitude, 14.3 millimeters; latitude, 32.0± millimeters; semidiameter 4.5 millimeters. Dimensions of right valve of a larger specimen: Altitude, 17.0 millimeters; latitude 38.2±millimeters; semidiameter 5.0 millimeters.

Cotypes: U. S. Nat. Mus. No. 352291.

Type locality: No. 3733, three-fourths of a mile west of Shell Bluff, Shoal River, Walton County, Fla.

Leda basilissa Gardner, n. sp., is a descendant of the group of Leda pharcida Dall of the Wilcox fauna, a shell of similar outline but not so large; it is more elongated transversely and the characters of lunule and escutcheon are similar, but the surface is more sharply sculptured.

The types are badly mutilated, but the shell is so unlike anything closely allied in time or space that it seems worth while to bring even the imperfect material to light.

Occurrence: Shoal River formation, locality 37335. Leda acuta (Conrad)

Plate II, Figures 13-16.

1832. Nucula acuta Conrad, American marine conchology, p. 32, pl. 6, fig. 3.

Not Nucula acuta Sowerby, Geol. Soc. London Trans., 2d ser., vol. 5, pl. 39, fig. 5, 1837.

1845. Nucula acuta Conrad, Fossils of the medial Tertiary of the United States, p. 57, pl. 30, fig. 2.

1846. Nucula carinata H. C. Lea, Am. Philos. Soc. Trans., new ser., vol. 9, p. 244, pl. 24, fig. 28.

1846. Nucula acutidens H. C. Lea, idem, p. 244, pl. 34, fig. 29. 1857. Nucula acuta Say. Tuomey and Holmes, Pleiocene fossils of South Carolina, p. 53, pl. 17, figs. 10-12. 1858. Leda acuta Emmons, North Carolina Geol. Survey Rept., p. 287, fig. 208 A.

1860. Nucula acuta Holmes, Post-Pleiocene fossils of South Carolina, p. 16, pl. 3, fig. 7.

1862. Leda unca Gould, Boston Soc. Nat. Hist. Proc., vol. 8,

p. 282.

1863. Nuculana acuta Conrad, Acad. Nat. Sci. Philadelphia Proc. for 1862, p. 581. 1863. Nuculana acutidens H. C. Lea. Conrad, idem, p. 581. 1863. Nuculana carinata H. C. Lea. Conrad, idem, p. 581. 1864. Nuculana acuta Conrad. Meek, Check list of the invertebrate fossils of North America, Miocene, Smithsonian Misc. Coll., vol. 7, No. 183, p. 5. (Name only.) 1864. Nuculana acutidens (H. C. Lea). Meek, idem, p. 5. (Name only.)

1864. Nuculana carinata (H. C. Lea). Meek, idem, p. 5. 1881. Leda jamaicensis D'Orbigny. Dall, Harvard Coll. Mus.

Comp. Zoology Bull., vol. 9, p. 124.

1882. Leda unca Gould. Verrill, Connecticut Acad. Arts and Sci. Trans., vol. 5, p. 572, pl. 58, fig. 41.

1884. Leda acuta (Conrad). Verrill, Connecticut Acad. Arts and Sci. Trans., vol. 6, p. 259, pl. 30, fig. 15.

1886. Leda acuta Conrad. Dall, Harvard Coll. Mus. Comp. Zoology Bull., vol. 12, p. 251; pl. 7, figs. 3a, 3b, 8. 1889. Leda acuta Conrad. Dall, Harvard Coll. Mus. Comp.

Zoology Bull., vol. 18, p. 438.

1889. Leda acuta Conrad. Dall, U. S. Nat. Mus. Bull. 37, p. 44, pl. 7, figs. 3a, 3b, 8; pl. 45, fig. 15; pl. 64, fig. 140. 1898. Leda acuta Conrad. Dall, Wagner Free Inst. Sci. Trans.,

vol. 3, pt. 4, pp. 592, 593.

1904. Leda concentrica (Say). Glenn, Maryland Geol. Survey, Miocene, p. 397, pl. 108, figs. 1, 2 (part).

1906. Leda acuta (Conrad). Clark, Maryland Geol. Survey, Pliocene and Pleistocene, p. 208, pl. 65, figs. 5-8. Conrad described this species in 1832, as follows: Shell ovate elongated, convex, with numerous regular concentric striae; anterior side slightly recurved and very acute at the extremity, and with the dorsal margin sunk so as to form a lanceolate depression; beaks behind the center; fosset very small and hardly oblique.

Habitat: Tertiary of Virginia.

Type: Academy of Natural Sciences, Philadelphia. The perplexing possibilities of variation in Leda acuta Conrad are due largely to its wide geographic distribution and to its great geologic range. The recent representatives present a comparative uniformity of development, whereas the Tertiary forms indicate a period of instability and evolution for the species. In the young the valves are higher, decidedly less convex, and the posterior dorsal margin straighter.

The great majority of the numerous Alum Bluff individuals commonly referred to Leda acuta have been distributed among Leda proteracuta and its subspecies, but there remain a few forms, most of them immature and badly worn, which probably represent a species distinct from both acuta and proteracuta but which have been tentatively included under the former. They are characterized by a relatively low, transversely ovate, trigonal outline and a concentric sculpture of very low, narrow, broadly rounded concentric ridges separated by little more than linear grooves, approximately uniform from the umbones to the ventral margin, slightly more compressed anteriorly, and not persistent across the rostrum. The normal sculpture of Leda acuta is a little more elevated and sharper, and there is no subspecies of proteracuta which combines so fine and close a sculpture with one so much compressed.

Occurrence: Chipola formation, localities ?2213P, 2564P, 3419P, ?71515.

Outside occurrence: Miocene: Calvert formation, Virginia; St. Marys formation, Virginia, North Carolina; Yorktown formation, Virginia, North Carolina; and Duplin formation, North Carolina, South Carolina, Georgia. Pliocene: Waccamaw formation, North Carolina, South Carolina; Caloosahatchie formation, Florida; and Croatan formation, Virginia, North Carolina. Pleistocene: Maryland, North Carolina, South Carolina, Florida. Recent: Rhode Island to Sombrero, in 7 to 225 fathoms.

Leda proteracuta Gardner, n. sp.
Plate II, Figures 17-18

1898. "Leda acuta Conrad." Dall, Wagner Free Inst. Sci. Trans., vol. 3, pt. 4, p. 592 (part).

Not Nucula acuta Conrad, American marine conchology, p. 32, pl. 6, fig. 1, 1832.

or

Shell rather small, delicate, polished, broadly and smoothly rounded in front of the umbones, narrow and cuneiform behind them. Umbones low, flattened upon their summits, the apices obtuse, incurved, and feebly opisthogyrate, submedial slightly anterior in position. Lunule narrow, lenticular, defined by the obtuse angulation of the shell and by the abrupt change in the character of the concentric sculpture. Escutcheon broad, produced to the posterior extremity of the shell, very finely and sharply striated. Rostrum acutely rounded even to the tip, thrown into relief by the obscure depression in front of it and in the majority of forms by the absence of the concentric sculpture which ornaments the greater part of the disk. Concentric sculpture developed to a greater or less degree over the disk; umbones finely and sharply ridged, the ridges broadening and becoming more obtuse away from the umbones but persisting as a rule to the ventral margin, most elevated medially, usually obsolete upon the keel and more or less obsolete upon the depression in front of the keel and often upon the anterior portion of the disk as well; the ridges numbering normally from 15 to 20 if persistent to the base, separated on the medial portion of the shell by interspaces of about their own width but more crowded ventrally. Ligament internal, lodged in a minute chondrophore sunk deep beneath the umbones. Dentition normal for the group, the anterior series including approximately 17 teeth, the posterior approximately 12; teeth delicate, compressed, elevated in the medial portion of each series, especially of the posterior, fine and crowded near the chondrophore, slightly Ʌ-shaped, the angle directed toward the umbones. Muscle and mantle scars obscure because of the high polish of the interior. Anterior adductor moderately large,

51459°-26-2

irregular in outline, placed just within the distal extremity of the hinge; posterior adductor much smaller, narrow, elongated in the direction of the dorsal margin. Pallial sinus short, broad, ascending, obtusely truncate at the extremity. Pallial line moderately distant from the basal margin.

Dimensions: Altitude, 2.8 millimeters; latitude, 5.0 millimeters; semidiameter, 1.5 millimeters. Type: U. S. Nat. Mus. No. 352292. Type locality: No. 7257, Sexton's marl bed, Tenmile Creek, Calhoun County, Fla..

Leda proteracuta is one of several species and subspecies included in the reference labels within the confines of that protean species Leda acuta Conrad. It is quite possibly the ancestor of Conrad's species and resembles its descendant in the range of variation. It is, however, constantly smaller than Leda acuta, more delicate, and as a rule relatively higher. The few individuals in the Chipola which it has not seemed advisable to separate specifically from Leda acuta have a lower, more compressed sculpture, uniformly close over the medial portion of the disk though weakening laterally.

Leda proteracuta, s. 1. includes those forms that are characterized by a wide, finely striated escutcheon and a sculpture of more or less obtuse concentric ridges, rarely persistent across the rostrum, commonly obsolete toward both the anterior and the posterior lateral margins and in some specimens restricted to the tips of the umbones, the ridges usually of low or moderate elevation and fairly close and regular in spacing, some of them conspicuously coarse and distant toward the umbones and others narrow, subacute, and quite closely spaced. The individuals in which the sculpture is conspicuously coarse, conspicuously fine, or conspicuously absent are excluded from Leda proteracuta S. S. The coarsely sculptured individuals are segregated under the subspecies dystakta. As in the still more distantly sculptured Leda diphya, the sculpture of dystakta becomes abruptly finer, closer, and commonly less regular upon the ventral portion of the shell. Leda dodona Dall is closely related to these coarser peripheral members, but it is more compressed toward the umbones and the ornamentation upon the escutcheon is irregular and more or less obsolete. The individuals in which the sculpture is restricted to the tips of the umbones and to crowded incrementals toward the ventral margin of the adults are segregated under the subspecies leita. These forms are for the most part more delicate and highly polished than is normal for the species. Those individuals that are characterized by a relatively fine, close, subacute sculpture have been segregated under diamesa. Through diamesa the species Leda proteracuta s. 1. is related to the still more finely, sharply, and regularly sculptured Leda leptalea and through Leda leptalea in turn to Leda canonica meiopykna and