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



2. ALBURNELLUS UMBRATILIS, Grd. 



SPEC. CHAR. Head constituting about the fifth of the whole length. Posterior extremity of the maxillary extending to a 

 vertical line drawu at the anterior rim of the orbit. Diameter of the eye entering three times and a half in the length of the 

 B ide of the head. Anterior margin of dorsal fin nearer the extremity of the snout than the fork of the caudal. Insertion of 

 ventrals nearer the extremity of the snout than the base of the caudal. Pectorals not reaching the insertion of the ventrals. 

 Dorsal region greyish brown ; flanks silvery grey ; belly reddish yellow. 



SYN. Alburnus umbratilis, GRD. in Proc. Acad. Nat. Sc. Philad, VIII, 1856, 193. 



This is a shorter and deeper species, and which might easily be mistaken for a Luxilus, so 

 striking is its general resemblance with small specimens of the latter genus. The greatest 

 length is about three inches ; the greatest depth being equal to the length of the head, and 

 contained five times in the total length. The lateral line, though running along the fourth 

 row of scales from the insertion of the ventrals, is more deflexed upon the abdomen than in A. 

 dilectus; the longitudinal rows of scales being fourteen in number. 



D 1, 8 + 1 ; A 1, 11 + 1 ; 5, 1, 9, 8, 1, 6 ; V 1, 8 ; P 13. 



The anal fin is nearly as long as deep, and longer than the dorsal ; its anterior margin is 

 placed a little behind the posterior margin of the dorsal. The tips of the ventrals overlap the 

 vent, nearly reaching the anterior margin of the anal. 



The color of the dorsal region is of a greyish brown tint ; the sides being of a silvery grey, 

 and the belly dull reddish yellow. The fins are olivaceous tinged with greyish. 



List of specimens. 



ALBURNOPS, Girard. 



GEN. CHAR. Body slender and compressed, protected with large and deciduous scales, which are deeper than long, and 

 posteriorly furrowed. Snout rather blunt and thick, overlapping the lower jaw, which is slightly shorter than the upper. Eye 

 large. Gill apertures separated beneath by a narrow isthmus. Dorsal fin higher than long. Insertion of ventrals placed 

 somewhat behind the anterior margin of the dorsal, else in advance of it. Caudal fin deeply furcated. The pharyngeal bones 

 resemble, by their configuration, those of Allmrndlus. The teeth themselves are of the prehensile kind of the hooked type, 

 with a narrow and sometimes contorted grinding surface. They are disposed upon a double row of two and four : 2 | 4 4 | 2, 

 or 1 | 44 | 2. 



SYN. Alburnops, GRD. in Proc. Acad. Nat. Sc. Philad. VIII, 1856, 194. 



Thus we see that a marked difference between Alburnops and Alburnellus consists in the 

 presence of a grinding surface to the teeth in the former, and which is absent in those of the 

 latter. 



This genus may furthermore be distinguished from Alburnus and Alburnellus by a smaller 

 mouth and by a thickening of the snout, which overlaps slightly the lower jaw, contrary to 

 what is the case in Alburnus and Alburnellus. In that respect, Alburnops will remind us of some 

 species of Hyborliynclius. The eye is large ; a very narrow isthmus separates the gill apertures 

 beneath. The insertion of the ventrals takes place under the anterior margin of the dorsal fin, 

 which resembles that of Alburnus and Alburnellus. 



