J 56 



IOWA GEOLOGICAL SURVEY 



acterized by abbreviate, stumpy proportions, and by a very 

 oblique line of insertion in the integument, are referable with 

 considerable probability to the posterior dorsal fin. They con- 

 trast strongly with the group of slender, elongate and tapering 

 spines represented by C. formosus, sculptus, depressus, venustus, 

 vetustus, denticulatus and numerous others, which evidently be- 

 longed to the first dorsal fin. The distribution of spines pertain- 

 ing to this genus in the Lower Carboniferous of this country is 

 shown by the following table : 



LIST OF SPECIES OF CTENACANTHUS OCCURRING IN THE MISSISSI- 



PPIAN SERIES. 



Name of Species 



O 



c 







O 



o 











M 



'5 



& 



p 



D 







"S 



O 



^ 









to 





« 



m 



W 



-*3 



CO 



1. Ctenacanthus coxianus St. J. and W 



2. decussatus Eastm 



3. depressus Newb 



4. longinodosus Eastm 



5. lucasi Eastm 



6. sculptus St. J. and W 



7. semicostatus (St. J. and W.) 



8. solidus Eastm 



9. spectabilis St. J. and W 



10. varians St. J. and W 



11. venustus Eastm 



12. (?) burlingtonensis St. J. and W. 



13. gradocostatus St. J. and W 



14. acutus Eastm 



15. cylindricus Newb 



16. excavatus St. J . and W 



17. " keokuk St. J. and W 



18. xiphias (St. J. and W. ) 



19. costatus Newb . and W 



20. ' ' deflexus St. J. and W 



21. gemmatus St. J. and W 



22. gurleyi Newb 



23. harrisoni St. J. and W 



24. littoni Newb 



25. pellensis St. J. and W 



26. angulatus Newb. and W 



27. canaliratus St. J. and W 



28. ' ' similis St. J. and W 



x 



X 

 X 



