54 PALEONTOLOGY OP OHIO. 



which here inhabited the shallows of the incoming sea of the Carbonifer- 

 ous age. In the limestones which form the open sea deposits of this 

 age, no traces of this fossil have yet been discovered. In the specimen 

 from which the drawing was made for the figure now given, the denticu- 

 lation is remarkably regular and exact. The litliographer has, however, 

 failed to represent this with accuracy. 



Ctekacanthus fukcicakinatus (n. sp.). 



Plate LIX., Figs. 3-3 c. 



Spine of medium size, robust; 8 to 10 inches long, 1^ inches wide. 

 Section near summit compressed, with flattened and nearly parallel sides, 

 near base oval. Basal portion smooth or longitudinally striated, rounded 

 below and thin from the expansion of the medullary cavity. Line sep- 

 arating the plain from the ornamented surfaces very oblique and sig- 

 moidally curved. Exposed portion of spine covered with" numerous 

 strong, more or less flattened and pectinated longitudinal costse, many of 

 which are dichotomously forked near the base. 



Toward the summit of the spine, there are about 1.5 of these costse. 

 Near the base they are much moi'e numerous from bifurcation. Those 

 near the anterior and posterior margins are fine, those occupying the 

 middle of each side more than twice as broad. The posterior face is 

 flattened so as to form a distinct angle with the sides, but is raised along 

 the median line in a strongly-marked but rounded ridge. 



The most striking features in this spine are the obliquity of the line of 

 contact between the exposed and buried portions, the bifurcation of the 

 rounded longitudinal ribs, and the general, but inconspicuous pectina- 

 tion. This is well shown in the enlarged view of three of the costfe 

 giveii in Plate LIX., Fig. 2 c. 



These spines are found so associated with the teeth of Orodiis varia- 

 bilis as to make it extremely probable that they belonged to the same 

 fish. There are also found with them quantities of dermal tubercles 

 which are undoubtedly those of this species of Ctenacantlius. Some of 

 these are represented, somewhat enlarged, in Fig. 4. They are obscurely 

 rhomboidal in outline and marked with a few coarse furrows and ridgres. 

 From the association of these fossils we are justified in concluding that 

 we have in them the teeth, spines, and dermal tubercles of one of the 

 sharks that inhabited the Lower Carboniferous seas. These are all the 

 really bony portions of most Selachians and all that are generally fossil- 

 ized ; but with these, in the present instance, are numerous traces of 



