of Cliinaxodus a/u/ Jaiiassa. ."{2.'} 



luuked upon as the principal or primary dental nricans ; the 

 other kind or the secondary, in the two genera, resemble each 

 other just as closely as do the primary ; and it is interesting 

 to tind that these secondary teeth agree pretty closely with 

 some of those included in the genus Petalodus of authors, only 

 they are oblique. 



In rlanassa the association of tliese Petalodontoid teeth with 

 the primary ones is too oljvious to be called in question. In 

 this form the two kinds are actually lound arranged in order 

 side by side. This is pi'oved by the specimens already re- 

 ferred to and by Munster's excellent figures. The Petalodon- 

 toid form has likewise been obtained associated on the same slab 

 with the primary teeth of CUmaxodus. We have in our pos- 

 session a small slab, not so large as the palm of the hand, on 

 which there arc seven primary teeth, three or four of Avhich 

 lie in their natural position. On this slab there are likewise 

 three of the Petalodontoid form, two being in contact with the 

 primary teeth, and apparently not far removed from their 

 original position. 



Hix or seven other specimens of these secondary teeth have 

 occurred scattered in the same shale in which the primary teeth 

 are found. The secondary teeth have a certain resemblance 

 generically to the primary teeth, and speciiically they have cha- 

 racters in common with their respective primary teeth. Never- 

 theless they are scarcely generically distinguishable from the 

 Petalodus of authors, though they are, as already stated, oblique. 



Having said thus much with respect to the external charac- 

 ters of the teeth themselves in the two genera in question, Ave 

 must now make some remarks about their arrangement in the 

 mouth. In Janassa it is clearly demonstrated, both by the 

 specimens and figures before alluded to, that the teeth are 

 similarly arranged in both the upper and under jaws. In this 

 genus they are placed in slightly arched transverse rows, the 

 largest symmetrical primary tooth being situated on the me- 

 dian antero-posterior line, and projecting a little in advance 

 of the others. On each side of this there are two similar teeth, 

 but somewhat less, the outside one being twisted obliqni'ly ; 

 the row is then terminated on either side by one of the Petalo- 

 dontoid form. There are therefore seven teeth in each row, 

 including both kinds — five primary, two secondary. Miinster 

 represents five or six such rows in close succession from back 

 to front, the teeth and rows gradually diminishing in size 

 forward. It is evident, then, that the arrangement of the 

 buccal armature luore closely resembles that of the Kays than 

 the Cestracionts or Sharks; and, indeed, notwithstanding the 

 difference in the teeth themselves, in their arrangement they 



