attaches to the Plagopteriiwe as the only type of fishes not known from 

 other waters than those of the Colorado basin. 



PLAGOPTERUS, gen. nov. 



Pharyngeal teeth, 2.5 4.2, raptorial uncinate, without masticatory 

 surface. A terminal maxillary barbel. Scales, none; lateral line well 

 developed. Dorsal fin with a strong spine composed of two, the posterior 

 received into a longitudinal groove of the anterior. Ventral fins origin- 

 ating (in the type species) a little anterior to the line of the dorsal, 

 attached to the abdomen by a wide basis and length of inner radius* 

 Superior labial fold continued round the end of the muzzle. 



This genus resembles Meda, Girard, in the presence of the dorsal spine, 

 the aJhesion of the inner border of the ventral fin, and the absence of 

 scales, and differs in the presence of barbels, and the inner dental series 

 being 5 4 instead of 4 4. Physiognomy of RMnichthys. 



PLAGOFTERUS ARGENTISSIMUS, sp, nov. 



This is a small fish of slender proportions, with a rather broad head, 

 with slightly depressed muzzle overhanging by a little a horizontal 

 mouth of moderate size. The caudal peduncle is of medium depth, and 

 the caudal fin is deeply forked. The eye is somewhat oval, and enters 

 the length of the side of the head 4.2 times, and the interorbital width 

 1,5 times. The greatest depth (near the ventral fin) enters the total 

 length nearly six times, or five and three quarters, exclusive of the caudal 

 fin. The latter measurement is four times the length of the head. The 

 origin of the dorsal is entirely behind the proper basis of the ventral ; its 

 first spine is curved and longer than the second, and its basis is inter- 

 mediate between the base of the caudal and the end of the muzzle. The 

 dorsal rays behind the spine have the basal two-thirds to one-half 

 thickened and completely ossified, the articulated portions issuing from 

 the apices of the spines. Radial formula, D. II. 7 ; C, 19 ; A. I 10 9 ; 

 V. 2. V ; P. 16, The first or osseous ray of the anal is rudimental ; the 

 fifth spinous ray of the ventral is bound by nearly its entire length to the 

 abdomen by a membrane. The pectoral rays from the second to the 

 sixth exhibit a basal osseous spinous portion, which is not nearly so 

 marked as hi the ventral?. The pectorals reach the basis of the latter. 



The lateral line is complete and is slightly deflexed opposite the dorsal 

 fin. The lips are thin, and the end of the maxillary bone extends to the 

 line of the front of the orbit. Total length M. 0.071 j ditto to middle of 

 basis of caudal fin .0565 ; ditto to anterior basis of anal fin .040 ; ditto 

 to basis rentral .021 ; ditto of head .0145 ; of muzzle .004 ; width at 

 posterior nares .006 ; at middle of pterotic .0078. Color, pure silver 

 for a considerable width above the lateral line. Dorsal region somewhat 

 dusky from minute chromatophora?. 



Numerous specimens from the San Luis Valley, Western Colorado, 



