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DE. A. SMITH AVOODWAHD OX 



[vol. lxxii r 



c entral cusp is much enlarged and elevated, and begins to be some- 

 what laterally compressed, with sharp anterior and posterior (outer 

 and inner) edges ; but the lateral extensions of the tooth, although 

 attenuated, still retain the characteristic anterior (outer) buttresses, 

 the apical ridge throughout their length, and the typical root (b ). 

 In the new specimen of Edestus the same enlargement of the 

 central cusp with reduction of the lateral extensions has progressed 

 so far that the central feature predominates immensely, while the 

 diminutive lateral parts curve backwards along the modified root 

 to clasp the next successional tooth (c). In typical Mdestus the 

 tooth is almost entirely a laterally-compressed central cusp, while 

 the clasping root is excessively enlarged (d). 



Diagrammatic sketches of half of a lateral' tooth of Campodus 

 variabilis, upper vieiv (a), ancl-symphysial teeth of Campodus 

 variabilis (b), Edestus newtoni (c), and Edestus minor (d), 

 left side vieiv, to shoiv progressive modification. 



A. B. C. D. 



[to = longitudinal ridge.] 



There seems thus to be no doubt that the small teeth of the 

 Campodus type occurring with the new fossil really belong to it, 

 and a question arises as to how the species represented by this jaw 

 shall be named. Campodus (1844) is an older generic term than 

 Edestus (1856). but it is evident that the teeth to which its 

 definition applies belong to more than one genus : for the sym- 

 physial teeth of Campodus variabilis, as made known by Eastman, 1 

 must be regarded as generically distinct from those of the specimen 

 now described, while the former must have been arranged as a 

 single row only in one jaw, and as a paired row in the opposing 

 jaw ; whereas in the Yorkshire teeth the surfaces of wear show that 

 there must have been an unpaired median row in each jaw. As 

 the latter arrangement has already been proved by Hay to charac- 

 terise Edestus, and as the symphysial teeth in the new fossil 

 merely differ from those of the typical Edestus in the relatively- 

 small size and extension of the root, I propose to regard it as 



1 Bull. Mus. Comp. Zool. Harvard Coll. vol. sxxis (1902) p. 58. 



