212 Marsh, description of anew Enaliosaurian 



fin in the Ichthyosaurus.^^* The absence of any lateral compression in 

 the present remains, together with their sisse and proportions, 

 prove conclusively that they cannot be brought under the excep- 

 tion which Prof. Owen makes of the terminal caudal vertebrae of 

 the Ichthyosaurus ; and hence the application of his rule would 

 separate them from that genus. 



The points of similarity, then, between these vertebrse of the 

 ^o^awrws, and those oHhe Ichthyosaurus, which they most resem- 

 ble, clearly indicate that they belong to the same natural group 

 of marine reptiles, and to the same order; while the differences 

 which exist between them seem to be sufficiently numerous and 

 important to authorize the conclusion that they are generically 

 distinct ; as might naturally be expected from the vast periods 

 of time that separated their existence. 



Since the genera of Enaliosaurians from the secondary forma- 

 tions, although contemporaneous, differed so widely in form and 

 structure, analogy would lead us to infer that a Palaeozoic repre- 

 sentative of the family would present still more marked peculiarities 

 in these respects. It is, therefore, particularly interesting to find 

 indications of so strong a resemblance between this primitive sau- 

 rian and the more recent Ichthyosaurus. These fossils, however, 

 present some features of a lower and more ichthyic type of struc- 

 ture than that genus possessed, and it is not unlikely that other 

 parts of the skeleton would show a wider divergence. 



These vertebrae of the Uosaurus, although the only remains of 

 the genus at present known, are so characteristic and well pre- 

 served that they afford considerable evidence in regard to the 

 structure and habits of the animal to which they belonged. 

 They indicate that this reptile, like the later Enaliosaurians, was 

 of great size,* air-breathing, cold-blooded, and carnivorous ; that 

 it was aquatic, and probably marine, inhabiting the sea or es- 

 tuaries; or possibly, as might be inferred from the place of 

 its entombment, the mouths of rivers flowing into the sea.f The 



* Report on British Fossil Reptiles, Part I, page 102. 



♦ If we suppose the number of vertebrae and the relative length of the 

 head of this saurian to have been the same as the Ichthyosaurus, its entire 

 length must have been between twelve and fifteen feet, which is at least 

 three times the extent of any reptile hitherto found in Palaeozoic strata. 



t Although the strata which contained the vertebra are probably 

 fluviatile or estuary deposits, this would not preclude the possibility of 

 their containing marine remains; as the waters from which they were 

 precipitated were undoubtedly so connected with the sea that an occasion- 

 al transfer of the inhabitants from one to the other might readily be made. 

 Analogous cases are not uncommon at the present time. 



