94 



MAEINE EEPTILES OP THE OXFOED CLAY. 



skeleton of MurcBnosaurus dnrohrivensis (R. 2863), since no well-preserved examples 

 of these bones in the type species (31. leedsi) are contained in the collection. In 

 M. leedsi the somewhat imperfect and badly-preserved atlas and axis have been 

 described by Professor Seeley *, and, so far as can be seen, differ in no important 

 points from those just noticed (PL IV. fig. 1). The remainder of the cervical region 

 (PI. IV. figs. 2-4; PL V. figs. 1-3 ; PL VI. figs. 4, 5; text-figs. 50, 51) is characterised 

 by the large number (about 41) of vertebrae composing it and the greater relative 

 length of the centra compared with those of the cervicals in Cryptocleidus and 



Text-fie. oO. 



Anterior cervical vertebra of Murmiosaurus durohrivensis : A, from left side ; B, from behind. 



(E. 2863, about nat. size.) 



a.s., anterior zygapophysis ; n.c, neural canal ; n.s., neural spine ; p.z., posterior zj-gapophysis ; 

 >•./., facet for rib ; s., neuro-central suture. 



Tricleidus : measurements will be given under the different species. The articular 

 ends of the centra are a rounded oval in outline, with the transverse diameter a little 

 longer than the vertical — this difference being less in the anterior than in the posterior 

 cervicals : there is a slisrht flattenins; beneath the neural canal. The articular 

 faces are gently concave and are surrounded by a sharply defined rounded border ; 



* " On 3Itci-(enosaunis leedsi, a Plesiosaurlan from the Oxford Clay," Quart. Journ. Geol. Soc. vol. xxx. 

 (1874) p. 200. 



