280 



U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



lateral line is likewise deflexed upon the abdominal region, and nearer the insertion of the 

 ventrals than the base of the dorsal. 



The color of the dorsal region and upper surface of the head is blackish brown, whilst the 

 sides of the head and the flanks exhibit a metallic yellowish white tint speckled with black. A 

 black streak may be observed along the upper region of the flanks, just above the lateral line, 

 and partly covering it. The fins are greyish olive ; the ventrals and pectorals being somewhat 

 more yellowish or else lighter than the rest. 



References to the figures. Plate LX, fig. 5, represents Ricliardsonius lateralis., size of life. 



Fig. 6 is a dorsal scale. Fig. 7, a scale from the lateral line. 



abdominal region. 



List of specimens. 



Fig. 8, a scale irom the 



LUXILUS, Rafin. 



GEN. CHAR. Body very much compressed, and deepest upon the middle of its length. Head proportionally small and com 

 pressed like the body. Mouth small, terminal ; when it is shut, the lower jaw fits into the upper one without protrusion of the 

 snout ; but when the mouth is partly open, the lower jaw appears longer than the upper. Eyes quite large. Isthmus small. 

 Caudal fin furcated ; insertion of ventrals situated in advance of the anterior margin of the dorsal. Scales large ; lateral line 

 forming a very open curve, convex downwards. Pharyngeal bones much stouter superiorly than inferiorly ; a slight expansion 

 may be observed upon the convexity of these bones, extending upwards. The teeth are of the bruising kind of the hooked type, 

 with a slight hook and a well developed grinding surface, both edges of which being strongly crenated. They are disposed upon 

 a single row of five, thus : 5 5. The three uppermost (sometimes the upper two only) stand out in bold relief from the line 

 of the br&amp;gt;ne. 



SYN. Luxilus, RAFIN. Ichth. Ohiens, 1820, 48. GRD. in Proc. Acad. Nat. Sc. Pliilad. VIII, 1856, 202. 



This is one of the most characteristic genus of North American cyprinoid, and altogether 

 misunderstood by Heckel; for, Cyprinus chrysoleucus , Mitch., which he places in his genus Leu- 

 cosomus, is generically distinct from Leuciscus pulcliellus of Storer, as I have had the opportunity 

 to ascertain. The diagnosis given of Leucosomus by its author, and the figures representing the 

 pharyngeal dentition, leave no room for doubt. Leucosomus, therefore, is not synonymous with 

 Luxilus, but was really established upon a species most intimately related to the one yet unpub 

 lished, and which is the type of the genus Cheilonemus. The latter, therefore, must give way 

 to Leucosomus, a circumstance unavoidable and very much to be regretted, for it complicates the 

 synonymy of both Luxilus and Leucosomus. It will include such species as are congenerical 

 with Luxilus chrysocephalus of Eafinesque, and Cyprinus crysoleucas of Mitchill. 



1. LUXILUS OCCIDENTAL-IS, Grd. 



SPEC. CHAR. Body rather elongated, sub-fusiform in its outline. Head constituting about the fifth of the total length. 

 Snout sub-conical, rather tapering. Gape of the mouth oblique. Posterior extremity of maxillar bone extending to a veitical 

 line which would intersect the hind nostril. Eye large and circular ; its diameter entering four times in the length of the side 

 of the head. Anterior margin of dorsal fin nearer the insertion of the caudal than the extremity of the snout. Origin of 

 ventrals nearer the insertion of the caudal than the extremity of the snout. Anterior edge of anal fin equidistant between 

 the isthmus and the tip of the lower lobe of the caudal. Dark greyish brown above ; yellowish beneath, speckled with grey. 



SYN. Leucosomus occidentalis, B &. G. in Proc. Acad. Nat. Sc. Pliilad. VII, 1854, 137. 

 Luxilus occidentalis, GRD. in Proc. Acad. Nat. Sc. Pliilad. VIII, 1856, 203. 



