262 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



feot example, from the same horizon and locahty, is shown in our 

 plate 7, figure 7. In this, however, as in most examples of this 

 species and of Physonemus from the St. Louis Umestone, the fine 

 details of tubcrculate ornamentation have become obliterated. A 

 smaller and more arcuate spine, or rather, the distal portion of one, 

 presumably of the same species, is shown in plate 5, figure 4. Its 

 curvature and smooth oostae are suggestive of AcondylacantJius atten- 

 uatus Davis, from the Lower Carboniferous hmestone of Ireland, but 

 it has a naiTowcr transverse section, and is best regarded as a rather 

 strongly arched example of C. gracillimus. It is catalogued as No, 

 8101. 



LIST OF SPECIES OF CTENACANTHUS OCCURRING IN THE MISSIS- 

 SIPPIAN SERIES. 



1. C. coxianus St. John and Worthen Kinderhook; also Keokuk. 



2. C. dentssatus Eastman Isinderhook; also Keokuk. 



3. C. depressm Newberry I^inderhook limestone. 



4. C. longinodsus Eastman Kinderhook limestone. 



5. C. lucasi Eastman Kinderhook limestone. 



6. C. sculptus St. John and Worthen Kinderhook limestone. 



7. C. semicostatus St. John and Worthen Kinderhook limestone. 



8. C. solidus Eastman lOnderhook limestone. 



9. C. spectabilis St. John and Worthen lOnderhook Umestone. 



10. C. varians St. John and Worthen lOnderhook Umestone. 



11. C.venustus Eastman Kinderhook Umestone. 



12. C.(?) burlingtonensis St. John and Worthen BurUngton Umestone. 



13. C. gradocostatus St. John and Worthen BurUngton Umestone. 



14. C. acutm Eastman Keokuk Umestone. 



15. C. cylindrims Newberry Keokuk Umestone. 



16. C. excavatus St. John and Worthen Keokuk Umestone. 



17. C. keohuk St. John and Worthen Keokuk Umestone. 



18. C. xiphias St. John and Worthen Keokuk Umestone. 



19. C. costatus Newberry and Worthen St. Louis Umestone. 



20. C. deflexus St. John and Worthen St. Louis Umestone. 



21. C. gemmatus St. John and Worthen St. Louis Umestone. 



22 . C. gurleyi Newberry ^t. Louis Umestone. 



23. C. hanisoni St. John and Worthen St. Louis Umestone. 



24. C. littoni Newberry St. Louis Umestone. 



25. C. pellensis St. John and Worthen St. Louis Umestone. 



26. C. angulatus Newberry and Worthen Chester Umestone. 



27. C. canaliratm St. John and Worthen Chester Umestone. 



28. C. similis St. John and Worthen Chester Umestone. 



Genus PHYSONEMUS M'Coy. 



Syn. Xystracanthus Leidy; Drepanacanthus Newberry and Worthen. 

 The earUest and most primitive remams assignable to this "genus" 

 are found in the Kinderhook hmestone of the Mississippi Valley, where 

 they are accompanied by small spines of StetJiacanthus. The Bur- 

 Ungton species of both genera are considerably larger than those from 

 the Kinderhook, but they are feebly ornamented, and so too are the 



