ORDERS OF FISHES. 



159 



eighteen inches in length. Hitherto this genus has only 

 been found in the Devonian of North America. 



In the Carboniferous period the remains of Cestraioliori 

 are comparatively very abundant, though confined generally 

 to particular localities. The spines of tbe Carboniferous 



Fig. 522.— 1, Fin-spine of PZewracamf/ww (one of tlie Rays); 2, Gyracanthus; 3, Ctenacan- 

 thm; i, Tootliof Petalodus; 5, Psammodus ; 6, Ctenoptychiiis. All from the Carboniferous 

 rocks. 



strata have been referred to many genera, of which the most 

 important are Ctenacantlms (fig. 522, 3), Gyracanthus (fig. 

 522, 2), HomacantJiiis, Ora- 

 canthus, Onchtcs, Leptacanthus, 

 and Edestes. The fossil teeth 

 of the Carboniferous rocks 

 have also been referred to 

 many genera, of which the 

 more important are Cochliodus 

 (fig. 523), Deltodus, Psammo- 

 dus, Orodus, Petalodus (fig. 

 522, 4), Ctenoptychms (fig. 

 522, 6), Cladodus, Ccntrodus, 



Glossodus, Diplodus, Helodus, and Pdrodus. Three principal 

 types may be distinguished in these teeth. In one type 

 (the " Cochliodonts "), as in Cochliodus (fig. 523) ov Psam- 



conto7-his. 

 iferous). 



5-23. 



— Dental plates of Cochliodus 

 Mountain Limestone (Carbon- 



