190 [September, 



uniform greyish brown above, silvery along the middle of the flank and yellow- 

 ish beneath. 



Speo'mens of this species were collected by Dr. Geo. Suckley, under Gov. I. I. 

 Stevens, in Milk and Little Muddy rivers, tributaries of the upper Missouri. 



4. Leucosomus pallidus. This species has the same general physiognomy as 

 L. dissimilis. The scales of the back are likewise a great deal smaller than on 

 the flanks, but in totum they are larger than in the preceding species. The origin 

 of the ventrals is situated in advance of the anterior margin of the dorsal, a 

 feature that will enable us at once to discriminate between this species and L. 

 dissimilis. The dorsal region is greyish brown, the ventral region yellowish 

 white. A black spot at the base of the caudal, as well as upon the anterior 

 margin of the dorsal. 



Specimens were collected in Antelope Creek, Arkansas, by Dr. C. B. Ivcnnerly, 

 under Lieut. A. W. Whipple, U. S. A. 



5. Leucosomus incrassatus. Remarkable for its stout and short body and 

 well developed head, which constitutes a little more than the fourth of the total 

 length. The scales are proportionally smaller than in L. pallidus. 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. 



Collected twenty miles west of Choctaw Agency, by H. B. Mollhausen, under 

 Lieut. A. W. Whipple, U. S. A. 



The following genus, for which the name of , 



NOCOMIS 



is thought well appropriated, has a short, stoutish and compressed body? 

 covered with large scales. The ventrals are inserted opposite the anterior mar- 

 gin of the dorsal, mayhap a little anterior to it. The caudal is furcated. The 

 head is large, rounded upon the snout, which is declivous. The mouth is large 

 and terminal, the lower jaw being slightly overlapped by the upper. A barbel 

 upon the posterior extremity of the maxillary. Eyes small. Isthmus rather 

 wide. The pharyngeals are stoutish, somewhat expanded upon their convexity ; 

 expansion tapering off towards the tip of the upper limb, which is gently curved 

 inwards. The inferior limb is scarcely longer than the upper, looks more slender, 

 is flattened upon its extremity, which is turned outwards, causing a convexity 

 inwardly. The teeth are of "the voratorial kind of the hooked type, without 

 grinding surface. They are subcylindrical, acerated and hooked, disposed upon 

 a double series of one and four, in the following manner : 1 | 4 4 | 1. 



This genus is allied to Semodhis by its pharyngeal teeth, diifering chiefly by 

 its mouth, which is not so deeply cleft, and by its maxillary barbels, which are 

 absent in Scmotilus. 



NocoMis NEBRACENSis. It is a fish about four inches in total length, of a 

 uniform reddish brown hue above, and golden yellow beneath ; a blackish 

 streak along the middle of the flanks terminating into a black spot upon the 

 base of the caudal fin. The lateral line is nearly medial, being but slightly de- 

 pressed along the thoracic region. 



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

 late J. Soule Bowman. 



The genera brought together in this paragraph are numerous, and quite 

 as varied in their dentition as in the former group. They differ from the latter 

 by the absence of barbels. As in the preceding, the teeth are of the hooked 

 types, Avith or Ayithout grinding surface (^Denies uncinato-submolares et uncinato- 

 subconici), mostly of the raptatorial kind. In the majority of cases, the teeth 

 are disposed upon a double scries also. 



This and the former group ought to be subdivided in a natural method, which 

 is not our object now. Moreover, a thorough grouping of the American Cypri- 



