182 -[Septfmber, 



the lower jaw rounded instead of angular, and, generally speaking, the eye rather 

 large. 



1. Hybognathus argyritis. This species seems to come nearest to H. nuchalis, 

 Agass., than any of the following ones. The eye, however, is quite large, sub- 

 circular in shape, its diameter entering a little short of four times in the length 

 of the side of the head. The snout is rather pointed, and the mouth larger than 

 in the species enumerated further below. The largest specimens observed are 

 four inches and a half in total length. The dark stripe along the dorsal line 

 does not appear conspicuously here, but may be observed, as on all the others, 

 more or less distinctly. 



We have examined specimens collected in Milk River by Dr. Geo. Suckley, 

 under Gov. I. I. Stevens, and in the Arkansas River near Fort Smith, by Dr. 

 Geo. G. Shumard. 



2. Hybognathus evansi. May easily be distinguished from the preceding by 

 a much stouter head, more protruding snout, small mouth, smaller eye. The 

 opercle is as long as deep, subquadrangular, slightly emarginated behind, as in 

 the rest of the species. 



Collected at Fort Pierre, Nebraska, by Dr. John Evans. 



3. Hybognathus placitus. The general aspect is shorter than in any of the 

 preceding species. The snout is thickish, but less so than in//, evansi; the 

 mouth smaller also. The eye is circular, its diameter being contained over four 

 times in the length of the side of the head. The scales are also larger than in 

 IT. evansi. Greyish brown above, greyish silver along the middle of the flanks, 

 and metallic white or yellow beneath. 



Collected in the sluices of the Arkansas near Fort Makee ; brought home by 

 Lieut. E. G. Beckwith^ U. S. A. 



The fish described by Dr. Ayres, under the name of Gila microlcpidota, presents 

 such peculiarly shaped pharyngeal bones, that wedid not hesitate erecting it into 

 a distinct genus under the name of 



ORTHODON, 



in allusion to the erect form of its teeth. But to proceed more systematically: 

 the head is subconical, attenuated towards the snout. The mouth is below the 

 medium size, terminal, oblique, both jaws even ; no barbels of any sort. A 

 knob or tubercle upon the symphysis of the lower jaw, as in Hybognathus. Eye 

 of medium size. Isthmus small. Body subfusiform, having the aspect of the 

 Gilse, but the ventrals are inserted under the anterior margin of the dorsal fin. 

 The caudal is furcated. The scales are small ; the lateral line submedial, being 

 somewhat depressed along the middle of the abdomen. The pharyngeal bones 

 are thin, vertically elevated, or rather broad in the vertical direction, bent as 

 usual and widening towards the upper and inner limb, so as to be broadest there. 

 The lower branch is much narrower. The teeth are of the cultriform kind of 

 the grinding type, compressed, lanceolated, erect, very slightly bent inwards. 

 They are disposed upon a single row of five, thus : 5 5, the upper ones being 

 quite raised above the edge of the bone. 



Orthodon microlepidotus. Gila microUpidota, Ayres, Proc. Cal. Acad. Nat. 

 Sc. i. 1855, 21. 

 San Francisco, Cal. Dr. Newberry. 



The genus we next come to, and for which we have chosen the name of 



ALGANSEA, 



has features and characters altogether different from any known genus. The 

 head is subconical, more or less pointed, though rounded upon its peri- 

 phery. The mouth being of medium size, slightly oblique upwards, its angles 

 never extending beyond the anterior rim of the orbit, and destitute of barbels ; 

 the j-aws themselves terminate evenly. The eye is of moderate development. 



