176 A NEW FOSSIL PORPOISE FROM MARYLAND 



Vertebra. 



The vertebrae are especially noteworthy in that all the cervicals are separate. 

 As already stated, the vertebrae preserved comprise 6 cervicals and the centrum 

 of one other; 9 thoracics; 6 lumbars; and 5 caudals. All the epiphyses are free. 

 Many of them have been preserved, however, and have been glued to the centra. 



I 





Cervicals. 



Atlas (PL XIX, figs. 3-13). — The atlas is separate from the axis and nearly 

 complete. It has a maximum height of 64 mm. and a breadth of 76 mm. In 

 general form it most resembles the same vertebra in Delphinapterus, Sotalia and 

 Delphinus, among recent genera, but differs from all three in many of its charac- 

 ters. It is relatively short antero-posteriorly, the length being about one-fourth 

 the breadth. The anterior articular facets are large, moderately deep, and not 

 strongly divergent. They are separated below by a rather wide interval, 

 measuring about 19 mm. The neural arch is low, and is broad antero-posteriorly 

 and pierced on each side by a large elliptical foramen, the long axis of which 

 measures 11 mm. The foramen is completely surrounded by bone. A single 

 transverse process is present on each side of the centrum, about in line with the 

 junction of the middle and lower thirds of the anterior articular facets. The 

 process is short, stout, and strongly curved backward. 



The posterior articular facets are moderately convex and oblong, with a nearly 

 straight, vertical external border, which is distinctly marked off from the posterior 

 surface of the centrum. This posterior surface, external to the facets, is very 

 broad and nearly flat. Its free margin is very prominent and its outline arcuate 

 when viewed from the side. The margin joins the transverse process below. 

 Between the posterior articular facets is a concave, nearly horizontal facet 

 for the odontoid process of the axis. Below it, the posterior median portion of the 

 centrum is slightly prolonged obliquely downward and backward, and presents 

 on its posterior surface, on each side of the median line, a pair of shallow pits 

 resembling alveoli, and below them two short, acute projections. The neural 

 spine is very low, somewhat longer than the arch antero-posteriorly, and has a 

 nearly straight free border which is inclined downward anteriorly. 



Axis (PL XIX, figs. 3, 4).— The axis has a maximum height of 70 mm. and a 

 maximum breadth of 79 mm., while the greatest thickness, antero-posteriorly, is 

 about one-fourth the breadth, or 19 mm. In general form it closely resembles 

 the axis in Delphinapterus, though the transverse process is lower, and the neura 

 spine smaller and lower. The whole vertebra is less thick. . 



The anterior articular facets are large, pyriform, or oblong, and only slign y 

 concave. They are separated below by an interval of 28 mm. The neural arc 

 is broad and thin ; concave anteriorly and convex and oblique posteriorly. ^ 

 neural spine is a thick process, oblong in outline when viewed anteriorly, an^ 

 triangular when viewed laterally. The free margin is transverse and roun e u 

 In the median line anteriorly is a sharp longitudinal ridge, and posteriory 



