MAKYLAND GEOLOGICAL SURVEY 15 



Priscodelphixus grandaevus Leidy. 

 Plate XII, Figs, la, lb, Ic. 



Priscodelphinus grandaevus Leidy, 1851, Proc. Acad. Nat. Sci. Phila., voL v, p. 327. 

 Priscodelphinus grandaevus Cope, 1890, Amer. Nat., voL xxiv, p. 605, figs. 2a, 2b, 

 3a, 3b, 3c. 



Description. — A.n atlas vertebrae corresponds very closely in size and 

 appearance to the figures of Priscodelphinus grandaevus Leidy, published 

 by Cope. The anterior face is deeply concave. The articular faces for 

 the occipital condyles are concave, broader above than below and 

 inclined obliquely outward. The opening is roughly triangular. The 

 upper surface is thin and there is no elevation of the neural arch; 

 the top of the arch is marked by a low spine and on either side of this 

 is a large foramen. On the sides the transverse processes are bifurcate, 

 a broader process pointing upward and outward and a narrower one 

 outward and downward, the two processes are connected by a sharp 

 ridge and on either side of this are several small foramina for nutritive 

 vessels. The posterior face shows strong articular faces for the axis 

 and the lower surface of the inside of the ring shows an articular face 

 for a broad odontoid process; the articular surface covers about two- 

 thirds of the inner face of the lower portion of the ring and is marked 

 off from the anterior portion by a low rugose line. The lower face is 

 marked by a strong peg-like rugosity pointing backwards. There is no 

 trace of a tendency to coalescence of the cervical vertebrae. 



Measurements : 



Breadth across anterior face 75 mm. 



Height anterior face 45 mm. 



Breadth across transverse processes 91 mm. 



Occurrence. — Calvert Formation. ^ mile south of Chesapeake 

 Beach. 



Collection. — Maryland Geological Survey. 



Genus IXACANTHUS Cope. 

 This genus was described with /. coelospondylus Cope as the type. 

 The original generic description is as follows : " This genus is similar 

 to the next (Priscodelphinus) in the cylindric spinous character of the 



