56 PALAEONTOLOGY OF OHIO. 



LiSTRACAXTHUS HYSTRIX, N. AND W. 



Plate LIX., Fig. 5. 



The species represented in the figure cited above, is very common in 

 the Coal Measures of Indiana and Illinois, thongh but rarely seen in Ohio. 

 It will be found described in the Geological Report of Illinois, Yol. lY., 

 p. 372, Plate XI., Figs. 3, Za. In Indiana these spines occur so frequently 

 with the dermal tubercles of Petrodus that they are generally supposed 

 to belong to the same fish. While this may be possible, it should he said 

 that we have never yet found the tubercles of Petrodus in Ohio, while 

 Listraoantlius is not unknown here. 



Formation and Locality : Black shale over Coal No. 6, Perry County, Ohio. 



LiSTRACANTHtJS HiLDRETIII (ll. Sp.). 

 Plate LIX., Fig. 6. 



Spine of relatively large size ; nearly 6 lines broad, 2 inches from the 

 summit ; curved and sharply carinated, carinfB slightly granular ; convex 

 side strongly squamose . 



Only a single specimen of this spine is known, and that lacks the basal 

 portion. It is sufficient, however, to show that it was much broader, 

 more curved, and more strongly and sharply marked than even the largest 

 specimens of the common species, Z. hystrix. 



Formation and Locality : This specimen was found near Marietta, by the late Dr. S. 

 P. Hildreth, and is now in the Cabinet of Marietta College. 



OrTHACANTHUS GRACILIS (ll. Sp.). 

 Plate LIX., Fig. 7. 



Spine small and straight, about three inches long, very slender and 

 acute ; section circular at base, posterior face and sides flattened above ; the 

 angle inclosed by them set with acute, recurved, compressed dentich^- 

 throughout the upper two-thirds of the entire length ; surface smooth or 

 very finely striated longitudinally. 



These delicate spines might be supposed to represent the immature 

 state of 0. arcuatus, but it is hardly supposable that they should have 



