Dr. Harlan on a ncto Fossil Species of Ichthyosaurus. 413 



On a new extinct Fossil Species of the Genus Ichthyosaurus. 



Soon after writing my last paper on the Saurocephalus, my 

 attention was directed to a small fragment of petrified bone de- 

 posited in the collection of British fossils in the Philadelphia 

 Museum. 



This specimen was originally from Bath or Bristol, and is 

 easily recognised, at first view, for a portion of the dental bone 

 of some Saurian reptile ; though from the small size and crush- 

 ed state of the specimen, and from its being in some degree 

 imbedded in a matrix of calp, it was at first difficult to as- 

 certain to what genus it belonged. 



Nevertheless, an attentive examination of this portion of 

 dental bone, a little more than an inch in length, and con- 

 taining six teeth, enabled me eventually to ascertain the fol- 

 lowing facts. 



The remnant is six-tenths of an inch high, and five-tenths 

 broad at the alveolar aspect. The largest teeth (for they vary 

 in size) are '65 of an inch long, projecting three-tenths above 

 the bone; the projecting portion being marked with closely 

 arranged, longitudinal striae ; a few widely separated longitu- 

 dinal lines mark the buried portion of the tooth, and the whole 

 tooth is conoidal from the base to the apex. 



In the mode of dentition this animal resembles the crocodile; 

 but it differs in having the teeth set in a continued groove, in- 

 stead of separate alveoli. It varies from the Plesiosaurus in 

 the same respect, and in the teeth, though conical, being not 

 so long proportionably, nor in the same degree aduncate as 

 in that animal It should be remembered that the teeth of 

 animals of this order vary in the latter respect even in the 

 same jaw, as is particularly the case in the I. intermedins. 



Our specimen totally differs from the Saurocephalus, in 

 the relative size, form and proportion of the teeth and dental 

 bone, and in the bodies of the teeth not being approximated 

 or contiguous. 



It resembles the Ichthyosaurus in the relative proportions 

 of the teeth, in having them set in a groove, and in its mode 

 of dentition. It approaches most nearly to the 7. communis in 

 the general appearance of the teeth, but differs from that spe- 

 cies in their relative size and form ; these bodies being more 

 aduncate in the latter. 



It differed from all the four species in the greater relative 

 thickness of the dental bone. In fine, it no more resembles 

 these species, than they respectively resemble each other. 

 From these data I am led to believe the present specimen to 



have 



