204 [September, 



Besides the two species just referred to, the present genus will include : 



3. Sbmotilus ateomacclatus. Oyprinus airomaculatus, Mitch. Leuciscus airo- 

 muculatus of more moderu writers. Leuciscus iris, Val. in Cuv. ^- Val., Hist. 

 Nat. Poiss. sii. 1844, 255, pi. 496. 



4. Semotilus macrocephalus. Easily distinguished by its very large head 

 which forms more than the fourth of the entire length. Its body is very much 

 compressed and tapering posteriorly. The scales are more uniformly imbricated 

 than in S. airotnaculahis, in which there is a noted difference it that respect be- 

 tween the anterior and posterior portions of the body. The species of this 

 genus are generally very uniform ; the number of the rays of the fins hardly 

 undergoes any variation. In the present species they stand as follows : 



D 9+2 ; A 9 + 2 ; C 6, 1, 9, 8, 1, 5 ; V 8 ; P 15. 



Two rudimentary rays in front of both the dorsal and anal, one of which very 

 exiguous. Brownish grey above ; silvery white beneath. A black spot at the 

 base of caudal also. 



Specimens were collected at Fort Pierre, Nebr., by Dr. John Evans, U. S. 

 Geologist. 



5. Semotilus speciosus. A graceful and slender fish, subfusiform in its out- 

 line, the head, which is conical and pointed forwards, constituting exactly the 

 the fourth of the entire length. The ventrals are situated a little further than 

 in S. atromaculalits. The scales of the dorsal region in advance of the dorsal fin 

 are quite small ; and those on the thoracic region smaller than posteriorly along 

 the sides of the tail. 



There are thirteen rays in the pectorals ; the number of rays in the other fins 

 does not diifer from the preceding species. 



The dorsal region is reddish brown ; the abdomen is yellowish or whitish. A 

 black vitta extends from the nose across the face and eye to the base of the 

 caudal, where exists also a circular black spot, similar to the one upon the base 

 of the anterior margin of the dorsal. 



Collected in the Sweet Water, a tributary of Platte or Nebraska River, by the 

 late J. Soule Bowman, 



We come next to a small fish, constituting a new genus, not without analogy 

 with the Gudgeons, differing from the true Gudgeons, by the absence of barbels 

 either maxillary or buccal and a less prominent snout. We propose to call it 



TIAROGA, 



and characterise it as follows : Head small, subconical, depressed. Mouth 

 obliquely terminal, of moderate size and without barbels of any kind. Upper 

 jaw slightly longer than the lower. Eye of medium size. Isthmus very wide. 

 Body slender, subfusiform, compressed. Fins are well developed ; dorsal and 

 anal narrow and high ; caudal bifurcated. The insertion of the ventrals takes 

 place in advance the anterior margin of the dorsal. The scales are small ; the 

 lateral line, medial. The pharyngeals are similar to those in Gohio. The teeth 

 are likewise of the same character : slender, subcylindrical upon their base com- 

 pressed above, of the raptatorial kind of the hooked type, without grinding 

 surface and disposed upon a double row of one and three, thus: 1 | 3 3 | 1. 

 So far but one single species is known. 



Tiaroga cobitis. About two inches and a half in total length, the head 

 forming about the fifth of it. The eyes approximate the upper surface of the 

 head which is rounded. The upper regions are brownish, with small blackish 

 spots; the inferior regions are unicolor of a yellowish tint. A black spot upon 

 the base of the caudal fin. 



Specimens collected by John H. Clark, under Col. J. D. Graham, in the Rio 

 San Pedro, a tributary of the Rio Gila. 



