GENUS PLACOPHARYNX. 107 



Genus PLACOPHARYNX Co:pe. 



Placopharynx Cope, Proc. Am. Philos. Soc. Phila. 467, 1870. 

 Type, Placopharynx carinatus Cope. 

 Etymology, tt/Iu^, a broad surface ; (papvy^, pharynx. 



Suckers like Myxostoma iu all respects, except that the pharyngeal 

 bones are much, more developed, and the teeth reduced in number, those 

 on the lower half of the bone very large, 6 to 10 in number, nearly cylin- 

 dric in form, being but little compressed, and with a broad, rounded 

 or flattened grinding surface. The forms and positions of these en- 

 larged teeth vary greatly. In a specimen before me, the lirst tooth is 

 the highest and most compressed, its summit being rounded and then 

 abruptly truncate. The second tooth is notably shorter and thicker, 

 much larger, and rounded on top, the body of the tooth serving as a pe- 

 duncle for the swollen grinding surface. The third tooth is still shorter 

 and similar in form. The fourth tooth is similar to the first, being much 

 higher than the second and third, and flat on top. The others seem to 

 be irregularly alternated or arranged in pairs, a long one and a short 

 one, the long teeth in all cases being the most truncated, as if their sur- 

 faces had been most worn off. 



As I have at present no perfect specimens of this genus, nothing but 

 very young specimens, and pharyngeal jaws of adults, I cannot do better 

 than to copy Professor Cope's original description, which seems to be 

 an accurate one. I substitute the generic names used in this paper 

 {Myxostoma, etc.) for those used by Professor Cope (Ptychostoinus, etc.), 

 whenever a difference occurs : — 



"Allied to Myxostoma. The pharyngeal teeth much reduced iu num- 

 ber, only seven on the prosimal half of the bone, cylindric in lorm, with 

 a broad, truncate triturating surface. These i^iay against a broad, cres- 

 centic, chitin-like shield on the posterior root of the pharyngeal cavity. 

 Three divisions of the vesica natatoria. 



"With a great superficial resemblance to Myxostoma, the masticatory 

 apparatus is different from that of any Catostomoid form known to me, 

 and combines peculiarities observed in some forms of true Cyprinidw. 

 The chitin-like shield is found in some of the latter ; it is represented in 

 Catostomus, Myxostoma, and Carpiodes by a narrow and very thin pel- 

 licle of the same material, frequently interrupted in the middle line." 



But one species of the genus is known. It is apparently widely dis- 

 tributed through the Mississippi Valley and the Great Lakes, but its 



