TEICLEIDUS SEELETI. 157 



Murcenosaurus. The number of cervicals (assuming that the series collected is 

 complete, as it appears to be) is only tv^enty-five, or even less than in Cryijtocleidus, 

 and only little more than half the number in Murcenosaurus (44). The atlas and axis 

 (PL VIII. fig. 8) are similar to those o^ Murcenosaurus figured above (text-fig. 49), except 

 in some details : thus the hypapophysial ridge, though not so strongly developed in front, 

 extends quite to the posterior end of the axis. The rib of the atlas (PI. VIII. fig. 8, r^) 

 is much longer than in Murcenosaurus, though still much smaller than that of the 

 axis (r.2) ; the neural arches (at. a., ax.a.) are lower. The other members of the 

 cervical series are characterised by the possession of short centra (if anything, a little 

 shorter than in Cryptocleiclus), the articular surfaces of which are considerably broader 

 than high and rather strongly concave (PL VIII. figs. 8, 8 a, 8 b, 8 c, 8 d) with a deep 

 central pit ; the concavity is bordered by a well-developed rounded border. The upper 

 surface is slightly concave beneath the neural canal. The lateral surfaces of the centra 

 above the facets for the cervical ribs are concave both from before backwards and 

 above downwards ; the ventral face is, as usual, perforated by a pair of nutritive 

 foramina separated by a narrow ridge. 



The neural spines are relatively naxrower from before back than in Crypfocleidus, 

 and towards the hinder part of the neck also higher. The cervical ribs have a well- 

 developed anterior angle, a remnant of the hammer-head shape of the ribs in some of 

 the earlier Plesiosaurs : this angle is less developed or absent altogether in Cryptocleidus, 

 but is well-marked in Picrocleidus (see PL VII. fig. 5, a.p.). Behind the cervical series 

 there are two vertebrae in which the rib is borne partly on the centrum and partly on 

 the incipient transverse process of the arch; these may be called the pectorals. Behind 

 these, in the type specimen, follow five dorsals, all that remain of the rest of the 

 vertebral column except two small posterior caudals. In the pectorals and anterior 

 dorsals (PL VIII. figs. 5, 6, 7) the centrum becomes more nearly circular in outline as 

 we pass backwai'ds, and the nutritive foramina ascend to its sides, where they open 

 at the bottom of a well-defined depression. At the same time the ventral surface 

 becomes flatter, so that at the fifth (the last preserved) dorsal it is only slightly convex 

 from side to side (PL VIII. fig. 5) ; the articular faces continue to be deeply concave. 

 The transverse processes increase rapidly in length as they pass backwards ; the neural 

 spines are high and relatively narrow. 



Of the two small posterior caudals the anterior one is considerably larger at its 

 anterior than at its posterior end ; the neural arch seems to have been very small and 

 low, and was confined to the front of the centrum. On the sides there are prominent 

 facets for the caudal ribs. On the ventral surface there is on either side a strong; 

 rounded ridge cut away obliquely both in front and behind by the chevron facets ; 

 both between and above these ridges the body of the centrum is concave from side to 

 side. The second still smaller caudal also bears facets for ribs and chevrons. 



The shoulder-girdle (PL VIII. fig. 3 ; text-fig. 76) is typically Elasmosaurian, the 



