6 O. C. Marsh on the Remains of a new Enaliosaurian. 



absence of a lateral compression of the centers, which, in the 

 Ichthyosauri, marks the posterior caudal vertebrse. Both of the 

 fossils are somewhat injured on their inferior surfaces, and hence 

 it is impossible to ascertain from the specimens themselves 

 whether haeraapophyses originally existed. 



The following admeasurements were taken from the nearly 

 perfect vertebra of the Eosaurus. For the purpose of compari- 

 son, the corresponding dimensions of an anterior caudal vertebra 

 of an Ichthyosaurus are added. It will be seen that the most 

 marked differences are in the position and dimensions of the 

 pits for the articulation of the neural arch, and in the depth of 

 the terminal c """ ~ 



Transverse diameter of centrum on anterior 



Ditto on posterior surface, 



o inchiding the parapophyses, 



ero-posterior diameter on superior surface, 



Ditto on inferior surface, , . . , 



Ditto between centers of articular facets, , . . 

 Length of pits for articulation of neural arch, 



Ireadth' of ditto, 



Depth of ditto, 



ince between centers of ditto, . 



> and centers of parapophyses, 



The dimensions of the other vertebra of the Eosaurus, so far 

 *as they can be accurately ascertained, coincide almost exactly 

 with those given above. 



In the margin of one of the vertebrae there is an angular 

 notch, about a line in depth, which deserves to be noticed on 

 account of the importance attached to it by Prof Agassiz, who 

 first called the attention of the writer particularly to it. Its 

 position is in the upper part of the posterior terminal facet of 

 the centrum, behind and between the pits for the articulation of 

 the superior arch. From the margin, where it is deepest, it 

 extends for a short distance toward the center, and gradually 

 becomes obliterated (Plates I. and II. figure 1, c). On the anterior 

 surface of the same vertebra, at a point opposite and nearest to 

 this depression, there is an elevation, which in position and 

 dimensions apparently corresponds to it; and the two, when 

 taken together, naturally suggest that they may be the result of 

 some pressure applied to the anterior surface of the vertebra be- 

 fore it was in its present fossilized condition. Prof. Agassiz, after 



