1856.] 173 



ventrals is situated in advance of the middle of the dorsal. The tips of the 

 pectorals reach a vertical line drawn from the origin of the dorsal. 



D 15; A 10; C 4, 1, 8, 8, 1, 3 ; V 10 ; P ] 7. 



Thirteen rows of scales may be counted between the origin of the ventrals 

 and the anterior margin of the dorsal ; the lateral line running through the median 

 row. There are two rudimentary rays at the anterior margin of both the dorsal 

 and the anal, and one at the exterior margin of the ventrals ; these are all sum- 

 med up in the formula. 



Specimens of this species were collected in the Yellow Stone river, by Dr. F. 

 V. Hayden, and in the Missouri river at Fort Pierre, by Dr. John Evans. 



Now then, if the principles upon which the above generic divisions are based, 

 be sound, the species which still remain in the genus Catosiomus must be further 

 revised and arranged in smaller and more restricted groups. 



We propose to arrange under the head of 



MINOMUS, 



such species as are characterised by an elongated and fusiform body ; a head 

 longer than deep ; a dorsal fin either higher than long, or with both dimensions 

 equal. The lips laeing tuberculated, moderately bilobed. The pharyngeals not 

 expanded laterally, but considerably bent inwardly. The teeth compressed, 

 decidedly bicuspid, but the inner projection more developed than the outer. 

 The scales being nearly of the same size, but slightly smaller anteriorly than pos- 

 teriorly. 



1. MiNOMUs iNSiGNis. Caiostomus insignis, B. & G. Proc. Acad. Nat. Sc. Philad. 

 vii. 1854, 28. 



Inhabits the Rio San Pedro, tributary of the Rio Gila. 



2. MiNOMUs PLEBEics. Catostoiims plclcius, B. & G.Proc. Acad. Nat. Sc. Philad. 

 vii. 1854, 28. 



From the Rio Mimbres, Lake Guzman, Mexico. 



3. MiNOMus CLARKii. Catostomus darJcii, B. & G. Proc. Acad. Nat. Sc. Philad. 

 vii. 1854, 27. 



From the Rio Santa Crux. 



And then giving the name of 



ACOMUS 



to those species in which the head is very elongated, the dorsal fin higher than 

 long, and the scales much smaller upon the anterior region of the body than 

 upon the posterior. The lips being papillated and very deeply cleft. The 

 pharyngeals are gently arched and not expanded ; the teeth compressed and bi- 

 tuberculated, the inner projection conspicuous ; the outer one, obsolete, though 

 existing. 



1. AcoMus FORSTERiANus. Catostomusforsterianus, Rich. Faun. Bor. Amer. iii. 

 1836, 116. 



Inhabits British North America. 



2. AcoMUS AURORA. Catostoiuus aurora., Agass. Lake Sup. 1850, 360. PI. ii. 

 figs. 3 and 4. May not differ from the preceding. 



Lake Superior. 



3. AcoMus LATiPiNNis. Catostomus latipinnisj B. & G. Proc. Acad. Nat. Sc. Philad. 

 vii. 1853, 388. 



Rio San Pedro, tributary of Rio Gila. 



4. Catostomus (Acomus) guzmaniektsis, has the general physiognomy of A. 

 latipinnis, owing to the great development of its fins. Is, however, very readily dis- 



