O. C. Marsh on the Remains of a new Enaliosaurian. 5 



which served for their articulating surfaces. These depressions 

 are situated on the superior surfaces of the centrum, interme- 

 diate between the anterior and posterior margins of the extremi- 

 ties. They are circular in form, and sink directly into the body 

 of the vertebra ; instead of being elongated longitudinally, and 

 raised on ridges, as in the Ichthyosauri. The pits are about a 

 line in depth, and in the more perfect of the Ibssils are not in 

 their original position ; as a fracture in the upper part of the 

 centrum has pushed them obliquely apart, so that a line passing 

 through their centers would form an angle of about 30* with 

 the transverse diameter of the vertebra. The depressions oc- 

 cupy about one-third of the distance between the margins of the 

 articular extremities, indicating that the base of the neural arch 

 was of less antero-posterior extent than the centrum. The floor 

 of the spinal canal is narrow, being but five lines in breadth; 

 and its surface in the posterior vertebra is broken by the frac- 

 ture, previously mentioned, which passes lengthwise through its 

 "'■"'" "Is, but 



No neurapophyses were found with these : 

 ■~-! of the superior arch is indicated by the f- 

 Ifor its ' —' ■ ' 



faces which served for its attachment. Without doubt 

 fication was complete, since the neurapophyses are never 

 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 Ichthyo- 



•thec 



distant from the extremities of the vertical diameter (Plate'II. 

 figures 1 and 2, h and b'). Their position is near the margin of the 

 anterior articular surface, and the edges of these parapophyses. 

 make the transverse diameter of this extremity somewhat greater 

 than that of the corresponding posterior facet. At the surface of 

 the 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 sur- 

 faces ; but externally appear to be composed of radiating fibres 

 of osseous tissue, and without doubt served for the attachment 

 of muscles. These elevations resemble in form and position the 

 rudimentary transverse processes on the caudal vertebrae of the 

 Ichthyosaurus teyiuirostris, and this similarity affords some ground 

 for referring these fossils to the same part of the vertebral col- 

 umn. That their true position is in the anterior or central cau- 

 dal region, is further indicated by the absence from the centrum 

 of true costal surfaces, or articular depressions for the attach- 

 ment of ribs, which we should expect to find present in the cer- 

 vical or dorsal part of the spinal column; and also by the 



