CRYPTOCLEIDUS OXONIENSIS. 



17= 



nearly flat oval facet for the transverse process. External to this proximal thickening 

 they are somewhat compressed from before backvs^ards, and their upper edge bears a 

 sharp ridge which terminates externally in a slightly backwardly deflected crest. 

 External to this again the ribs are nearly circular in section ; they become very 

 little thinner towards their lower end, which terminates in a flat or slightly concave 

 surface probably tipped with cartilage in life. 



The ventral ribs (text-fig. 86) form a close plastron consisting of eight or nine 

 transverse rows of bones, each consisting of a median element (I) and three lateral 

 pairs (2, 3, 4), besides two posterior rows in which the median element is wanting. 



Text-fig. 86. 



Ventral view of plastron of ventral ribs of Crijptocleklus oxoniensis. (R. 2S62, -i- ntit. size.) 



pu., pubis ; p.r., forked end of posterior ventral rib ; pu.sijni., symphysis of pubis ; 



1, 2, 3, 4, median and three lateral ribs of a transverse series. 



The median bone of a row is oval or circular in section in its middle portion, 

 which is often much thickened ; towards the outer ends the bone thins down to a 

 point, and its anterior face at either end bears a flattened facet for union with the 

 inner end of the first lateral rib. This is pointed at both ends and forms a very open 

 S-shaped curve ; its inner end bears on its posterior face a surface for the overlap 

 upon the median bone, while its outer end has on its anterior surface a facet for the 

 reception of the inner end of the second lateral rib. This latter is similar to the first, 

 and the third difi"ers only in wanting the outer facet, the outer half being rounded or 

 oval in section and terminating in a point. There is no trace of any connection 

 with the true ribs. The two hinder rows differ from the others m not possessing a 



