210 Marsh, description of a new Enaliosmirian 



is indicated by the articular surfaces which served for its attach- 

 ment. "Without doubt its ossification was complete, since the 

 neurapophyses are never inferior in this respect to the body of the 

 vertebra. It is also probable that in the present case these parts 

 were anchylosed to each other and to their spine, as in the neural 

 arch of the Ichthyosaurus. 



A rudimentary transverse process, or exogenous tubercle, is sent 

 off from each lateral surface of the centrum, at points equidistant 

 from the extremities ofthe vertical diameter. Their position is near 

 the margin of the anterior articular surface, and the edges of these 

 parapophyses make the transverse diameter of this extremity some- 

 what greater than that of the corresponding facet. At the surface 

 ofthe vertebra, each of these tubercles is about six lines in diameter, 

 but they rapidly diminish in size as they extend outward, and at a 

 distance of one and a half lines from the centrum terminate in obtuse 

 points. They present no indications of articular surfaces; but exter- 

 nally appear to be composed of radiating fibres of osseous tissue, and 

 without doubt served for the attachment of muscles. These ele- 

 vations resemble in form and position the rudimentary transverse 

 processes on the caudal vertebrae of the Ichthyosaurus tenuirostris, 

 and this similarity affords some ground for referring these fossils 

 to the same part of the vertebral column. That their true posi- 

 tion is in the anterior or central caudal region, is further indicat- 

 ed by the absence from the centrum of true costal surfaces, or ar- 

 ticular depressions for the attachment of ribs, which we should 

 expect to find present in the cervical or dorsal part of the spinal 

 column ; and also by the absence of a lateral compression of the 

 centers, which, in the Ichthyosauri, marks the posterior caudal ver- 

 tebrae. Both of the fossils are somewhat injured on their inferior 

 surfaces, and hence it is impossible to ascertain from the specimens 

 themselves whether haemapophyses originally existed. 



A microscopic examination of the osseous structure of these 

 vertebrae of the Eosaurus exhibits well-marked reptilian char- 

 acters. The Haversian canals are few in number, but large in 

 size, as is usual in this class. The lacuna?, although somewhat 

 irregular in shape, are much elongated, and show very little re- 

 semblance to the quadrate or stellate form of the bone cells in 

 fishes. They are frequently arranged concentrically around the 

 Haversian canals, and their walls are almost invariably well defined. 

 Thecanaliculi, as in the Ichthyosaurus and Plesiosaurus, are not 

 numerous, but appear to be finer than those in most saurians. They 



