NO. 1875 NEW FOSSIL CETACEAN — TRUE 453 



The dimensions of the periotic are as follows : Greatest length, 

 42 mm. ; greatest breadth at posterior end, 27 ; length of anterior 

 petrous portion, 18; depth of the same, 11. 



Vertebra 



As already stated, an atlas and two thoracic vertebrae accompany 

 the mandible, and, from their size, complete ossification, and color, 

 appear to have belonged to the same individual. (PI. XLV.) 



The atlas resembles that of Eurhinodelphis. The articular facets 

 for the occipital condyles are large, broad, deep, and but little in- 

 clined outward. They are separated below by a space of about 17 

 mm. The foramen above these facets on either side is complete, 

 and of large diameter, and is situated nearly in the middle of the 

 length (antero-posteriorly) of the neural arch. The arch is com- 

 paratively narrow, thin anteriorly, but with a broad, concave surface 

 posteriorly in the median line above. The spine is rudimentary. 

 The posterior articular facets are large, nearly circular, flat, and 

 project strongly from the body of the vertebra. Below in the me- 

 dian line there is a broad, shallow concavity, indicating that the 

 odontoid process of the axis was large and prominent. There is 

 also a large median rugosity on the postero-inferior surface of the 

 vertebra, which represents the remains of a strong process which 

 extended below the body of the axis. On either side of the verte- 

 bra are two short, thick transverse processes superimposed, as in 

 Bwhinodelphis. 



The two thoracic vertebras are from near the posterior end of the 

 series, and probably belong near one another. The body of the 

 more nearly complete one, seen from the front, is broadly cordate in 

 outline. The inferior outline, seen from the side, is deeply concave. 

 The epiphyses appear to be thin. The transverse processes are 

 short, thick, directed outward, and somewhat expanded at the ex- 

 tremity. Their upper surface is nearly in line with that of the body 

 of the vertebra. The metapophyses are prominent, rather thin, and 

 rectangular. The anterior zygapophyses are large and only slightly 

 concave, and are placed obliquely. The posterior zygapophyses are 

 oval in form, and directed obliquely downward and outward. The 

 neural spine is somewhat incomplete, but was originally inclined 

 backward more or less. It is broad antero-posteriorly, with a thin 

 anterior edge, and quite thick posterior edge. 



The second thoracic vertebra (pi. xlv, figs. 5 and 6) is quite im- 

 perfect, lacking the whole of the neural arch and spine and one of 

 the transverse processes. The remaining process is similar in form 



