NOTE: Very small, rounded, globose, pale runts appear com monly with typical specimens. Their diagnostic characters are frequently modified. In field collections, such specimens are virtually impossible to identify. They should not be confused with other species or cast into the subgenus Hyalommina. Among collections of reared adults, gradations from typical males to atypical males closely approximating exceptionally small specimens of H. dromedarii are frequently seen. Such atypical specimens are obviously poorly nourished in the immature stages and show numerous indications of lack of proper development. If encountered singly, they would be most difficult or impossible to properly identify.

Figures 174 and 175, o, dorsal and ventral views
Figure 176, 9, scutum and capitulum, dorsal view

Figure 177,, genital area. A, partly engorged, B to D, outline and profile; B and C, partly engorged; D, fully engorged.

HY ALOMMA IMPRESSUM Koch, 1844.

(Figures 174 to 177)

THE WEST AFRICAN HY ALOMMA

NOTE: In literature on African ticks various subspecific designations of H. impressum apply actually to H. rufipes or to H. truncatum and are treated herein under those species. The "H. plumbeum impressum" of Soviet workers is H. rufipes. Koch's (1844) descriptions of H. impressum and of H. rufipes clearly distinguish these two species.

The H. impressum mentioned by Adler and Feldman Muhsam (1946,1948) for Palestine resulted from mistaken identity of H. rufipes (Feldman Muhsam 1954), as did Delpy's H. impressum (1946A,B) from Iran (Delpy 1949A,B). The H. impressum of Schulze (1918), from a single specimen collected from a horse in Macedonia, Greece, and presumed to have been carried there as a nymph on a migrating bird, is questionable; this record was repeated by Panda zis (1947).

DISTRIBUTION IN THE SUDAN

H. impressum is locally common on cattle in central Sudan west of the Nile. Numerous males and fewer greatly engorged fe males reach the Khartoum quarantine station on Darfur and Kordo fan cattle and many males are still attached when these cattle reach the Cairo abattoir. The West African hyalomma is not known to be established east of the Nile.

Darfur: Zalingei and Sibdo (common on camels and cattle, also occurs on horses; SVs).

Kordofan:

Khartoum:

Delami (cattle; SVS). El Obeid (camels, SVs).

See three paragraphs above.]

DISTRIBUTION

H. impressum is a West African tick that ranges eastward into the Sudan. It has not been found south of the equator, in the great northern deserts of Africa, or on the Mediterranean littoral.

Schulze 1919, and
Schulze and

WEST AFRICA: FRENCH WEST AFRICA (As H. impressum sp. nov.: Koch 1844. As H. aegyptium impressum typica: Chodziesner 1924. As H. impressum impressum: Schlottke 1930, and Kratz 1940. As H. savignyi intermedia: Girard and Rousselot 1945, and Rousselot 1946. As H. impressum: Rousselot 1953B). NIGERIA (As H. impressum: Unsworth 1952. Material in BMNH from Katagum; H. H. det.).

CENTRAL AFRICA: CAMEROONS (As H. impressum: Rageau 1951, 1953). FRENCH EQUATORIAL AFRICA (As H. impressum: Rousselot 1953B).

EAST AFRICA: SUDAN (As H. impressum: Hoogstraal 1954B. Feldman Muhsam 1954).

?UGANDA and ERITREA:

As H. impressum: Wilson (1949B) and Tonelli Rondelli (1930A). These may refer to H. rufipes or to H. truncatum._7

HOSTS

Domestic cattle are the chief hosts of H. impressum, and are mentioned by all authors. No other hosts have previously been reliably recorded. In Darfur, camels are frequently infested and horses are sometimes attacked.

Unstudied.

BIOLOGY

DISEASE RELATIONS

Unstudied.

IDENTIFICATION

Males: This handsome species is easily recognized and readily distinguished by the following combination of characters: (1) center of subanal shields posterior of central axis of adanal shields, (2) scutum regularly covered by deep, rather large punctations that often tend to obscure the long lateral grooves, and (3) distinctive narrowing of the scutal margin posterior of the lateral grooves, giving it a rectangular outline posteriorly.

A moderate amount of circumspiracular pilosity may in some specimens suggest H. rufipes. The festoons are more or less fused, but the central and two median pairs are always distinct. The scutum is dark reddish brown to black and the legs are brightly ringed. The comparatively narrow, elongate scutal shape is in contrast to the wide outline of H. rufipes; the rectangular pos terior margin is distinctive of H, impressum.

Females: Numerous, regular scutal punctations, similar to those of the male, are distinctive; in some specimens they are more superficial but still numerous. The genital apron is broad ly triangular in outline; it is composed of an anterior narrowly transverse (bulging) ridge and a posterior button (sloping or depressed) not so wide as the anterior ridge. With respect

to the outline and profile of the genital area of this species, no specimens observed during the present study conform to that illustrated by Delpy (19498, page 106), which is more narrowly triangular (equilateral) and gradually sloping in profile. A certain amount of circumspiracular pilosity is present in some females; differences in the genital aprons distinguish these specimens from females of H. rufipes, the scutal punctations of which may be quite similar to those of H. impressum.