408 EXPLOEATIONS ACEOSS THE GREAT BASIN OF UTAH. 



less generically, distinguished. The barbels, being only tags of skin proceeding from 

 the integument of the maxillary bones, have very little systematic value compared with 

 the barbels, and especially the maxillary Imrbels of the >Siluroids. As the above-men- 

 tioned dift'erences are those only whicli have induced ichthyologists to distribute them, 

 we have no hesitation in bringing the above-named genera together as closely-allied 

 members of the same subfamily. Alfjoma \Yiis indeed placed by Dr. Girard among the 

 Clwndrostomi, but he was probably led to that act by the consideration of the single 

 row of pharAnigeal teeth and the absence of barbels, and not on account of the pres- 

 ence of a cartilaginous sheath enveloping the lower jaw. Girard has expressly stated 

 tliat the sheath is not one of the essential characters of the group as understood by 

 him. Bleeker was therefore incorrect in ])lacing that genus in a gronj) of wliich the 

 presence of the cartilaginous sheath was the principal distinction. 



The following appear to be the distinctive characters of the genera above enumer- 

 ated : 



The genus Gohio as admitted l)y Heckel has a compressed and gradually-narrowed 

 head, with the dorsal surface transversely convex, and declining to the snoiit. The 

 ventral fi'iis are under the anterior rays of the dorsal fin. The scales are large, there being' 

 about forty in the typical species along the lateral line. The center of the eye is 

 behind the middle of the head. There are well-developed maxillary barbels. 



Tlie genus Semotihis of Rafinesque has a head much like that of the Gohiones, 

 but it is usually larger, and declines less toward the snout. The bases of the ventral 

 fins are more anterior, being almost entirely in advance of the dorsal fin. The scales 

 are comparatiAely small. The eyes are mostly or altogether in the anterior half of the 

 head. The Ijarbels are also somewhat smaller. The genns Leucosomus of Heckel and 

 Girard is strictly identical with this. 



In the genus Pogonkhthys as now restricted, the head is small, compressed, and 

 gradually narrowed to the snout; its dorsal surface is transversely convex, and declines 

 ([uite rapidly to the prominent snout. The periphery of the jaws is elongated-semi- 

 elliptical. The ventral fins are under the middle of the dorsal. The scales areof moder- 

 ate or rather small size. The eyes are almost entirely situated in the anterior half of 

 the head. The maxillary barbels are small. 



The genus I'latygohio is very nearly allied to royon/cJdJ/ys, but differs from it by 

 its broader head, the width at the occiput being only about a third less than the naked 

 portion of its dorsal surface ; the scales are also larger. 



Only one species of Platyyohio is known. Numerous specimens were collected on 

 Captain Simpson's expedition. 



PLATYGOBIO COMMUNIS, Gill. 



Synonymy. 



POGONICIITIIVS COMMUNIS Givanl, Researches upon C'ypriuoid Fishes, (sess. copj', p. 2),) in Proceedings of Academy of 

 Natural Sciences, vol. viii, p. 188, 18.5G; Girard, lelitliyolofji,- of Pacific Railroad Reports, p. 247, pi. Iv. 



The body is elongated, compressed, and gradually decreases in breadth from the 

 liead to the caudal fin. The dorsal outline, anterior to the dorsal fin, is slightly curved 



