156 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



"Les visceres rappellent ceux des cyprino'ides en ge'ne'ral, inais I'intestin, & cause de 

 ses nombreux replis, a eccore plus d'e'tendue. . . . Le foie se rdsout bieutot en 

 huile; la vessie adrienne est cominune'ment divise' en deux et communique avec le 

 Laut de I'cesophage comme dans nos cyprins." (VALENCIENNES, Hist. Nat. des Poissons, 

 xvii, pp. 423-424.) 



HYLOMYZON Agassiz, 1855. "The name of this genus is a mere translation of the 

 vernacular name of its type, the Mud-Sucker of the West, framed in imitation of 

 Petromyzon, but expressing its habits of living in the mud. The body is stout and 

 heavy in front, and tapers off rapidly from the shoulders towards the tail ; behind the 

 dorsal it is nearly cylindrical in form. 



" The short quadrangular head is broad and flat above, its sides are vertical. The 

 eyes are of moderate size and elliptical in form ; the superorbital ridges are elevated 

 above the general level of the head. The mouth is inferior, and encircled by broad 

 fleshy lips which are covered with small grains or papillae The lower lip is bilobed. 

 The dorsal is over the ventrals, and nearer the head than the tail ; its height and 

 length are nearly equal. The pectorals and ventrals are broad and rounded, the anal 

 fin is slender and reaches the caudal. The scales are largest on the anterior portion of 

 the body. They are slightly longer than high, 'the ornamental concentric ridges of 

 the posterior field are broader and farther apart than those of the lateral and anterior 

 iields ; those of the anterior and posterior fields rather remote, about equal in number. 

 Tubes of the lateral line arising from the centre of radiation. 



"The teeth are compressed, so that their sharp edge projects inwards; at the same 

 time they are slightly arched inwards and inserted obliquely upon the pharyngeal' 

 bones. They increase gradually in size and thickness from above downwards. The 

 masticating ridge of the teeth is transverse, compressed in the middle and sharp; its 

 upper and lower edges are rounded and more projecting, the inner point, however, more 

 projecting than the outer one." (AGASSIZ, Am. Journ. Sci. Arts, 1855, p. 205.) 



CATOSTOMUS Agassiz, 1855. "I have retained the name of Catostomus for the type 

 to which it was originally applied by Forster. The body is elongated, fusiform and 

 slightly compressed. The snout is short and blunt, and projects but little beyond the 

 mouth, which is inferior. The lower jaw is short and broad. The lips are fleshy and 

 strongly bilobed below ; their surface is conspicuously granulated or papillated. The 

 head is considerably longer than high. The dorsal is large and mostly in advance of 

 the ventrals; its length is greater than its height. The anal fin is long and slender, 

 and reaches the caudal. The sexual differences, so conspicuous in the genus Moxostoma 

 and Prychostoinus, are hardly to be noticed in this genus. The other tins are of moder- 

 ate size, and more or less pointed. 



" The scales are much smaller on the anterior than on the posterior portion of the 

 body ; nearly quadrangular, with rounded angles, but somewhat longer than high ; 

 the ornamental concentric ridges of the posterior field broader than those of the lateral 

 and anterior fields; the radiating furrows more numerous than in Hylomyzon and 

 Ptychostomus, and encroaches upon the lateral fields, where, in some species, they are 

 nearly as numerous as upon the anterior and posterior fields. Tubes of the lateral line 

 wider than in Hylomyzon and Ptychostomus, extending from the centre of radiation 

 to the posterior margin. 



"The pharyngeals are stout and compact, the outer margin not so spreading as 



