APHACTOCLEIDUS TERETIPES. 



611 



shows considerable flattening on the top. The anterior wedge-bone forms the lower 

 third of the cup, and the rim extends downwards to the base of the prominent 

 hyapophysial ridge (liy.r.). The lateral pieces of the neural arch of the atlas (at. a.) 

 are broken, but, from what remains, it is clear that they did not unite above but 

 continued back and fused with the anterior zygapophyses of the axis, thus enclosing 

 a small opening on each side between the arch of the axis (ax.a.) and the arch of the 

 atlas. In the axis there is a low neural spine (n.sp.) with an indifferently developed 

 ridge at its base. The posterior end of this spine is 1 cm. thick, and contains two 

 deep, semicircular facets separated by a vertical ridge (text-fig. 1, C). The neural 

 canal (n.c), in section, is an ellipse with the long axis vertical, and at the axis 

 end this elongation is more pronounced. The rib of the atlas (r.j) has evidently 



n.s 



CL7L 



a. a — 



Text-Fig. 2. 



Anterior cervical vertebra (sixth) of Apraetocleidus teretipes : A, from leftside; 

 B, from behind. (Type specimen V. 1091, \ nat. size.) «.«., anterior 

 angle of rib; «.«., anterior zygapophysis ; c.r., cervical rib; n.c, neural 

 canal ; n.s., neural spine ; p.z., posterior zygapophysis. 



been considerably smaller than the rib of the axis (r. 2 ), although both are now 

 incomplete. The facets for those ribs are not confluent, but distinctly, though 

 slightly, separated. The posterior face of the centrum (ax.c.) is much wider than 

 high, and the upper side, forming the floor of the neural canal, is quite fiat. 

 The central portion is gently concave, but between this part and the circumference 

 there is a convex portion and the rim is turned back, the reflection of the under 

 part being most pronounced. 



Besides the atlas and axis there are other twenty-seven cervical vertebrw (text- 

 fig. 2; Plate, fig. 3). In the measurements of the . centra, the proportions are 

 not found to differ in any essential from those of Crypto cleidus oxoniemis. The 

 ends of the centra are transversely oval, the upper part, forming the floor of the 

 neural canal (n.c), being flat or slightly concave. The ends are decidedly concave 

 in the centre, but convex and reflexed at the margins. The ventral side, between 



