FOSSIL FISHES. 53 



teeth, amoHg- wliicli are species of Petalodus, Cladodus, and Ctenopiij' 

 chius. 



Of these tlie largest and most abundant belong to a species of Petalo- 

 (7us, which seems to agree in all respects with P.AUeghaniensis, described 

 by Dr. Leidy, and lirst obtained from the Coal Measure limestones of 

 Pennsylvania. Two of these teeth are now figured, and they re])resent 

 fairly Avell the size and forms of tlie specimens found. It will be noticed 

 that in one of tliese the crown is higher, and the root lai-ger than in the 

 otlier. Tliese differences are not constant, however, and can hardly have 

 s]X'ciiie value. They are probably due to tlie positions held by the differ- 

 ent teetli in the extended series which formed the dentition of the fish to 

 wliich they belonged. 



In the Report of the Geological Survey of Illinois, several species of 

 Petalodus are described, one of which, P, desiructw^ is fi'oni the Coal 

 Measures. From its large size and peculiar root, this tootli was consid- 

 ered distinct from P. Alleghaniensis, but Mr. O. St. John, wlio has given 

 much study to the fish teeth found in Illinois and Iowa, regards them as 

 identical. This seems to me probable, but it is not yet proved by any 

 facts which have come under my observation. None of the specimens of 

 P. Alleghaniensis yet found in Ohio are more tlian half as large as some 

 of those from Sangamon County, or from Cassville, Illinois. Tliey differ 

 too, in tlie form of the root; the specimens from Ohio having more elon- 

 gated and narrower roots than the great teeth, witli spatulate, pointed 

 roots, which are found in the Coal Measures of Illinois. These difl:'erences 

 may be only local, however, and it is Cjuite possible that intermediate 

 forms will hereafter be found which shall connect the robust and power- 

 ful te«th of the West, with the smaller and more delicate forms which occur 

 in the Crinoidal limestone of Ohio. 



Ctenacantiius formosus, Newb. 



Plate LIX., Figs. 1-le. 



This fine species of CtenacantJius is described in Yol. I., Part IL, p. 

 328, of this Peport. The figure now given is taken from a very perfect 

 specimen obtained by M. C. Pead, Esq., from the Cuyahoga shale at War- 

 ren, Trumbull County. It illustrates the size, form, and markings better 

 than the figure before given, and much better than any verl)al description 

 could do. During the progress of the Survey, more or less perfect speci- 

 mens of this species were met with in various parts of the State, whei'e the 

 Waverly rocks were exposed, and it is evident that the shark which bore 

 them was the most connnon, and probably the most formidable of those 



