KEPOKT ON ICHTHYOLOGY. 405 



The mouth is terniiiial, small or moderate, the maxilliiry bones ceasing' under or 

 near the anterior marg-ins of tlie orbits; the periphery of the jaws is triangular, semi- 

 t'Uiptical, or oval. 



The jaws are covered by thin lips; the lower lips are separated at the symphysis 

 by a ^^^[de isthmus. There are no barbels. 



The branchial apertures extend forward to or beyond the vertical of the preoper- 

 culum, and are separated by a rather narrow istlnnus. 



The dorsal tin connnences near the posterior half of the body, or between the 

 snout and end of median caudal rays. There are about twelve rays. 



The anal is nearly intermediate between the bases of the ventral and caudal fins, 

 and is of nearly the same size as the dorsal. 



The pectoral tins are of moderate length, and their extremities are more or less 

 rounded, and not acute. 



The ventral iins are inserted under, or nearly under, the first rays of the dorsal 

 fin; the first rays are of nearly equal length. 



The pharyngeal bones are well developed, curved above, and with the peduncles 

 rather long or moderate. The teeth are compressed and hooked, with or without a 

 grinding'-surface, and disposed normally, in two rows; the primary one has four or 

 five teeth, and the secondary (or deciduous?) one or two. 



This genus belongs to a g-roup of genera of which the Leuciscus of Europe is the 

 type, and it is indeed very closely related to that genus. AJgansca of Girard is 

 scarcely distinct, differing- simply because of the pharyngeal teeth being confined to a 

 single row ; and it is by no means certain whether this is a true or permanent charac- 

 ter. To this genus Tlfioma also belongs the so-called Cheonda ceerulea of Girard, which 

 difters from Cheonda Cooperi (the type of the geniis) by its narrow suborl)itals. 



TIGOMA SQUAMATA, Gill. 



The body is robust and subovate, compressed, and very gradually diminishing in 

 width toward the caiulal fin. The dorsal and abdominal outlines are nearly equally 

 arched. The greatest height of the l)ody before the dorsal and ventral fins equal 

 tkree-tenths of the length from the snout to the end of the median caudal rays, and is 

 twice as great as the greatest width. 



The caudal peduncle is rather slender, and naiTowest between the anal and caudal 

 fins; the distance between the anal fin and the base of the caudal equals eighteen 

 hundredths of the total length; the height behind the anal twelve hundredths, and that 

 of its most slender pair ten hundredths. 



The head is conical in profile, acutely rounded anteriorly, and with the perij)hery 

 of the jaws elongated semi-elliptical. The jaws are even; the maxillary bones end at 

 the vei'tical of the anterior border of the eyes. The length of the head from the snout 

 to the margin of the operculum forms more than a quarter (twenty-eight hundredths) 

 of the entire length; the distance from the same place to the scaly nape exceeds a fifth 

 of the length. The dorsal surface of the head is posteriorly flattened, and anteriorly 

 becomes slightly convex; the outline of the naked portion is elongated sul)conical, and 

 gi-adually decreases in width; posteriorly equahng fifteen hunch-edths of the total 



