3S4 PALEONTOLOGY OF ILLINOIS. 



be impressed with their intimate relationship. It differs from C. apicalis 

 in its thinner crown, straight basal border, more slender and shorter 

 base, and greater number of serrations in the crest, also the absence of 

 pectiuationsin the coronal band. 



The original specimen described by Prof. Agassiz, (Pois. Foss., torn. 

 Ill, pp. 99, 173. tab. 19, f. 1, la,) belongs to the collection of Sir Philip 

 Egerton, which we were permitted to examine while it was in the pos- 

 session of Prof. Agassiz, who at one time had in contemplation the 

 revision of the fossil Selachians, in aid of which purpose both Lord 

 Enniskillen and Sir Philip had contributed the use of their valuable 

 collections, which were for a time at the Museum of Comparative 

 Zoology ; thus it was that we have eujoyed the rare privilege of studying" 

 material which has been rendered doubly valuable both on account of 

 its historical and scientific interest. The type specimen above referred 

 to was derived from the carbonaceous shales of the Coal Measures, 

 Staffordshire near Manchester, England. It presents very peculiar and 

 at the same time marked distinctive features which can scarcely be mis- 

 taken. A careful- examination of this specimen, and comparison with 

 that above described, leads to the recognition of affinities more nearly 

 allied to Chomatodus or Antliodus than to Ctcno^etalus and other thick, 

 long-based Petalodonts. The character of the basal region offers strik- 

 ing contrast to Ctenopetalus, and even the coronal region may be distin- 

 guished by its plane concave face — in the latter respect exhibiting 

 intimate relationship with the abbreviated forms of Chomatodus, and in 

 the former resembling both Chomatodus and Antliodus. 



Position and locality : In a calcareous bed holding a stratigraphic 

 position about one hundred feet above the Mahoning sandstone, Coal 

 Measures ; near Morgantown, West Virginia. 



GEmis POLYBHIZOD US, McCoy. 



POLYKHIZODUS WLLLL43ISI, St. J. and W. 



PI. X A, Tig. 23 i-Pl. XTTT, Fig. It. 



The collection of Dr. "Williams affords a single nearly perfect example 

 of u form of Polyrhisodus apparently specifically distinct from the seve- 

 ral forms at present known from our Carboniferous deposits. It is dis- 

 tinguished by its strong, robust crown, which presents a lenticular 

 outline, lateral extremities acutely rounded, the lateral diameter about 

 two and a half times greater than the hight of the concave face ; the 

 convex crown-face is worn down, reducing the elevation "»t least one- 

 third, the present crest line well-defined, but formiug an obtuse angle, 

 the triturating surface occupying its entire area, to the broadly and 



