DEVONIC FISHES OF THE NEW YORK FORMATIONS 151 



that the supporting palato-pterygoid cartilage was of the usual pattern 

 found in all Dipnoans. This cartilage, when ossified, is commonly known 

 as "upper dentigerous bone"; the fact that it is unossified in Arthrodires 

 agrees with other evidence pointing to their lesser specialization as com- 

 pared with Ctenodipterines. 



The restoration of the upper dentition of M. variabile, shown in 

 the above figure, requires no additional explanation beyond that given in 

 the introductory account of Arthrodires. It may profitably be compared 

 with text figure i8, which is reproduced from a photograph of the actual 

 dental plates. The retention throughout life of two pairs of palato-ptery- 

 goid dental plates in this family, corresponding to an evanescent stage of 

 Neoceratodus, is regarded as a primitive characteristic. Hence, in so far as 

 the dentition is concerned, members of this family recall ancestral conditions 

 more distinctly than either Dinichthys or Coccosteus. 



Genus binomylostoma Eastman 

 A genus transitional between Mylostoma and Dinichthys, as its name 

 implies, and partaking of the characters of both. Mandibles with slightly 

 prehensile symphysial beak, and broad, flattened, regularly concave func- 

 tional margin, showing marks of contact with dental plates of the opposite 

 jaw, the latter essentially like those of Mylostoma. Vomerine teeth 

 subtrihedral, slightly prehensile. 



Dinomylostoma beecheri Eastman 



Plate 14, figures 5, 6 ; plate 15 ; text figure 32, 33 



1906 Dinomylostoma beecheri C. J?. Eastman. Am. Jour. Sci. v. 21, ser. 4, 



p. 83, text fig. 2 (No description) 

 1906 Dinomylostoma beecheri C. R. Eastman. Mus. Comp. Zool. Eul. 



5°7 p- 23, pi- I. fig- 4, s; pi- 2, fig. 13, 14, 16, 17; pi- 4, S 



1906 Dinomylostoma beecheri L. Hussakof. Am. Mus. Nat. Hist. Mem. 

 9, p. 119, 123 



The specific characters of this form are included in the foregoing 

 generic diagnosis. It may be remarked, however, that its particularly dis- 

 tinctive feature consists in the acute termination of both mandibles and 



