156 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY III. 



"Les viscares rappellent ceux des cyprinoides en g6n6ra\, mais I'intestin, a cause de 

 ses norubreux replis, a eccore plus d'6tendue. . . . Le foie se rdsout bientCt en 

 builo; la vessie adrenne est commuu^ment divis6 en deux et communique avec le 

 baut de I'cesophage commc dans nos cyprins." — (Valenciennes, Hist. Nat. des Poissous, 

 xvii, pp. 423-424.) 



Hylomyzon Agas^iz, 1855. — "Tbe name of tbis f^euus is a mere translation of tbe 

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

 Petromyzon, but expressing^ its babits of living iu tbe mud. Tbe body is stout and 

 heavy in front, and tapers off rapidly from tbe sboulders towards the tail ; bebind tbe 

 dorsal it is nearly cylindrical in form. 



" Tbe sbort quadrangular bead is broad and flat above, its sides are vertical. The 

 eyes are of moderate size and elliptical iu form ; tbe superorbital ridges are elevated 

 above tbe general level of tbe bead. Tbe mouth is inferior, and encircled by broad 

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

 The dorsal is over tbe ventrals, and nearer tbe bead than tbe tail ; its height and 

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

 tin is slender and reaches tbe caudal. The scales are largest on the anterior j)ortion 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 

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

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



"The teeth are comi)ressed, so that their sharp edge projects inwards; at tbe same 

 time they ;ire slightly arched inwards and inserted obliquely upon the pharyngeal 

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

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

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

 projecting than the outer one." — (Agassiz, Am. Journ. Scl. Arts, 1855, p. 205.) 



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

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

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

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

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

 bead 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 tin is long and slender, 

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

 and Ptychostomus, are bardly to be noticed iu this genus. The other tins are of moder- 

 ate size, and more or less pointed. 



" Tbe scales are much smaller on tbe 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 tbe lateral 

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

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

 nearly as numerous as upon tbe anterior aud posterior fields. Tubes of tbe lateral line 

 wider than in Hylomyzon and Ptycbcotomus, extending from tbe centre of radiation 

 to the posterior margin. 

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



