252 



U. S. p. R. R. EXP. AND SURVEYS— ZOOLOGY — GENERAL REPORT. 



3. LEUCOSOMUS INCRASSATUS, G r d. 

 Plate LXI, Figs. 1—6. 



Spec, Char.— Head rather large, »ub-conical, constituting about the fourth of the total length. Eye moderate sized ; its 

 diameter entering » little over five times in the length of the side of the head. Gape of the mouth slightly oblique ; posterior 

 extremity of ma.xillar bone reaching a vertical line drawn within the anterior rim of the orbit. Anterior margin of dorsal fin 

 equidistant between the fork of the caudal and the extremity of the snout. Insertion of ventrals situated in advance of the 

 anterior edge of the dorsal. Dark greyish above, light greyish beneath, with a black spot at the anterior edge of the dorsal. 

 Other fins unicolor, light yellowish olive. 



Srs.— Leucosomus incrassalus, Gbd. in Proc. Acad. Nat. Sc. Philad. VIII, ]856, 190. 



The specips here referred to is remarkable for its stout and short body and well developed 

 head, which constitutes a little less than the fourth of the total length. The fork of the caudal 

 is according to the pattern of that of L. pallidus. The dorsal and anal fins are somewhat deeper 

 than long. The pectorals and ventrals are small ; the tips of the latter, when directed back- 

 wards, are far from attaining to the vent. Nothing is more uniform than the formulae of the 

 fins of the various species of this genus : 



D 2, 8 + 1 ; A 2, 8 + 1 ; 5, 1, 9, 8, 1, 6 ; V 1, 8 ; P 17. 



As to the scales, they are moderate sized, sub-circular, nearly as large on the dorsal region 

 as on the flanks, exhibiting radiating furrows upon their posterior section alone. 



Dark greyish above, light greyish beneath, with a yellowish hue all over the head and body. 

 A black spot upon the anterior margin of the dorsal ; none upon the caudal. 



Inferences to the figures. — Plate LXI, fig. 1, represents Leucosomus incrassatus, size of life ; 

 fig. 2 being a section of the body across the line of greatest depth. Fig. 3, a dorsal scale. 

 Fig. 4, a scale from the lateral line. Fig. 5, a scale from the abdominal region. 



List of specimens. 



4. LEUCOSOMUS MACROCEPHALUS, Grd. 



Si'Ec. Char. — Head very large, rather elongated, forming more than the fourth of the total length. Snout sub-conical, 

 thickish. Eye moderate; its diameter entering about six times in the length of the side of the head. Gape of the mouth 

 slightly oblique; posterior extremity of the maxillary extending to a vertical line drawn across the anterior rim of the pupil. 

 Anterior margin of dorsal lin e(iuidistant between the extremity of the snout and the fork of the caudal. Insertion of ventrals 

 situated in advance of the anterior edge of the dorsal. Brownish grey above, silvery white beneath ; a l^bk spot at the base 

 of the caudal and anterior edge of the dorsal. 



Syn. — Sanoliliis macrocqihalm, Giio. in Proc. Acad Nat. Sc. Philad. VIII, 1856, 204. 



It is by a mere accident that this species formerly appeared under the head of Semotilus. It 

 may easily be distinguislied from its congeners by its very large head, which forms more than 

 the fourth of the entire length. Its body is very much compressed and quite tapering posteriorly. 



