JUN 16 1902 



]sj"o. 3. — Some Carboniferous Ccstraciont and Acanthodian 

 Sharks. By C. R. Eastman. 



Coincident with the marked increase of Pelmatozoa and certain fam- 

 iUes of Brachiopods during the Lower Carboniferous all over the world, 

 a race of sharks armed with crushing teeth suddenly acquired dominance, 

 became exceedingly diversified, and finally all but passed away towards 

 the close of the Paleozoic. Of the very extensive group represented by 

 the Cochliodontidse and Cestraciontidfe, which is at least as ancient as 

 the Devonian, only one genus, the so-called Port Jackson shark, survives 

 at the present day. With this all of the fossil forms agree in having a 

 similar but more or less specialized dentition, in consequence of which 

 this creature stands in the same relation to the host of Carboniferous 

 sharks with ci'ushing teeth that Nautilus does to fossil Cephalopods. 



Some interesting specimens from the Carbonifei'ous described in the 

 present paper throw new light on the structure and relations of Campo- 

 dus and the series of Edestus-like forms, all of which are to be regarded 

 as members of the Cestraciontidse. Spines belonging to the first and 

 second dorsal fins of Ctenacanthus, from the Kinderhook limestone of 

 the Mississippi Valley, and new species of Acanthodes from the Coal 

 Measures of Mazon Creek, Illinois, ai'e here illustrated and described 

 for the fii'st time. A list is also given of the fossil vertebrate fauna 

 known to occur at the Mazon Creek locality, including some spe- 

 cies not previously reported. 



L ON THE NATURE OF EDESTUS AND RELATED FORMS. 



Notwithstanding the extensive literature concerning the peculiar 

 ichthyic remains known as Edestus, Helicoprion and the like, their 

 nature, functions, and relations are admitted by most authors to be still 

 highly problematical. Occurring as they do singly, and always in the 

 detached condition, these objects have been most frequently looked upon 

 as Selachian fin-spines, although their correspondence to dental structures 



VOL. XXXIX. — NO. 3 



