VEETEBEATES. 3S3 



Agassiz, exhibiting precisely similar basal characters, while the crown 

 differs chiefly from the typical species, as well as from C. Stevensoni, in 

 the less acuruiuate and minute serratiou of the crest, and fewer indica- 

 tions in the coronal belt; the base is relatively stronger than that of 

 the latter species, while it nearly agrees in this particular with the 

 typical European form. It is also much smaller, the largest examples 

 attaining scarcely half the size of either of the above named forms. 



Position and locality : Chester limestone ; Chester, Illinois ; upper 

 fish bed. 



Ctenoptychixjs Stevensoni, St. J. and W. 



PI. XH, Fig. 15. 



Teeth small, delicate, in outline polygonal. Convex crown-face semi- 

 <elliptical, plane or slightly arched laterally, regularly and considerably 

 arched along the crest, which slightly projects beyond the line of the 

 nearly straight basal angle, which latter is bordered by a narrow coro- 

 nal belt composed of two or three folds, which are geutly deflected at 

 the lateral angles, forming a baud continuous with that of the opposite 

 faee^ -concave face irregularly and broadly oval, gently and somewhat 

 angularly depressed in the middle, basal border strongly produced aud 

 sharply inbeveled below, composed of four or five wide imbricating 

 folds, widening at one extremity, nearly straight in the median region 

 And abruptly rounded into the lateral extremities ; the crest line is 

 strongly and somewhat irregularly arched, slightly acumiuate, and 

 ■acutely denticulated, the denticulations more or less regularly diminish- 

 ing in size from the strong median one towards theextremities, of which 

 f here are six or seven in either side, faintly striated along the abraded 

 ■edge; both coronal faces enveloped in a dense, polished enamel like 

 layer. The fome is proportionately slender, considerably less in lateral 

 diameter than the crown, eccentric, as seen from below, the region 

 beneath the .convex crown-face narrowing towards one extremity, gently 

 depressed and defined above and below by an obtuse angle, the opposite 

 face relatively low, deeply channeled beneath the produced coronal bor- 

 der, inferior surface relatively wide, irregularly rectangular in outline, 

 beveled to an acute edge in nearly the same horizontal plane as the 

 •crown. 



The description of this elegant form is based upon one of three speci- 

 mens which were discovered by Prof. J. J. Stevenson in the Coil 

 .Measures of West Virginia. It differs so widely from any species thus 

 far made known from the American Carboniferous series, that it scarcely 

 requires a detailed comparison to distinguish it. When, however, com- 

 parison is made with tlte type of the genus G. apioalis, Ag., (not G. api- 

 •calis referred to by McCoy, Brit. Palse. Foss., p. G20,) one cannot fail to 



