OF THE ELASMOBRANCHS. 



75 



indication of any articulation, and the cartilages are directed outward and forward. If 

 it is supposed that there was originally an articulation which has become effaced during 

 fossilization, we must make the unlikely assumption that the two cartilages Lave been 

 removed from their natural, posteriorly directed position and made to take new posi- 

 tions, symmetrica] on the two sides. 



The size of the nasal capsules furnishes no certain evidence of the batoid nature of 

 this animal. The hammerhead sharks have these larger than any of the rays; and it 

 is not improbable that Tamiobatishad its nasal capsules developed for some such function 

 as is subserved by this organ in the modern hammerheads. Tamiobatis must have been 

 quite different in many respects from anything now in existence. Dr. Eastman has 

 figured two structures which he has identified as the postorbital arches. He states that 

 each of these appears to he (ait oil' from the rest of the skull by a, small cleft; but he 

 says these clefts have every appearance of being fortuitous. These are alike on the 

 two sides, and to me they appear wholly natural and as the indications of articulations. 

 As Dr. Eastman suggests, the portions thus cut off do not appear to be metapterygoids ; 

 and we are left in the dark as to their real nature. It appears to me not improbable 

 that the structures outside the clefts are portions of the palatoquadrate arch, attached 

 to the postorbital process, as it is in some modern sharks. At all events if appears that 

 we are hardly justified in concluding that the fossil in question, which lived in the 

 middle of the Palaeozoic era, belongs to a group which, so far as we have any reliable 

 evidence, did not come into existence until the Mesozoic era was well advanced. 



