626 WILLIAM R. SMELLIE ON 



most highly specialised Elasmosauridse the modifications of the shoulder-girdle that 

 have taken place are in the direction of increased rigidity in that region. In the 

 course of this series of changes there is a tendency to the reduction of the clavicular 

 arch accompanied by, and consequent upon, the increasing size and importance of 

 the ventral ramus of the scapula." In Apractocleidus the fusion of the scapulae, of 

 the coracoids, and of the scapulae to the coracoids (text-fig. 7) provides the maximum 

 rigidity ; while the increase in size of the ventral ramus of the scapula has resulted 

 in the forward growth of the scapulae beyond even the anterior tip of the clavicular 

 arch, which in this way becomes quite invisible from below (Plate, fig. l). In 

 Cryptorfeidus the clavicles protrude beyond the anterior end of the scapulae (text- 

 fig. 7, B; Andrews, 1910, p. 179, text-fig. 88) to a varying extent, but in Apracto- 

 cleidus they lie functionless (hence the generic name) wholly within the visceral 

 surface of the scapulae. Further, the slight increase in the angle of the glenoid 

 would enable the shOulder-girdle to receive better a directly forward thrust from the 

 head of the humerus. 



In the pelvis, excepting the ilia, where ligamentous union is most suitable, the 

 rigidity of the shoulder-girdle is repeated, being brought about by fusion of the 

 pubis and ischium, and by a long contact in the median symphysis. 



The high degree of ossification present, and the elongation of processes — for 

 example, the dorsal rami of the scapulae and the postero-external processes of the 

 coracoids (text-fig. 7) — -are indications of a higher organisation. Seeley stated (1874, 

 p. 449), when discussing the Plesiosaurian pectoral arch, that " the only general 

 conclusion at which I have arrived is that Plesiosauria, in common with all similar 

 groups, show, in the newer rocks as compared with the older ones, a greater amount 

 of ossific energy, probably coincident with higher organisation, which manifests 

 itself in more perfect ossification of the bones, elongation of the processes, and 

 blending of subordinate with the principal ossific centres." Again, in a paper on the 

 shoulder-girdle in Sauropterygia, Seeley (1892, p. 148) states: "In the shoulder- 

 girdle nothing but continued ossification apparently is needed to convert the Liassic 

 Plesiosaurian into the Oolitic and Cretaceous Elasmosaurian type." Judged by the 

 above criteria, Apractocleidus can be fairly claimed to be a more highly organised 

 type than any of the related Oxford Clay Plesiosaurs. 



The habits of Apractocleidus probably differed in no essential from those of 

 previously described Oxford Clay Plesiosaurs (Andrews, 1910, pp. xv-xvii). The 

 paddles, with their strength and symmetry of outline and deep rugosities for muscle 

 attachment, speak eloquently of powerful swimming. The comparatively short neck, 

 usually associated with fast swimming, and probably accompanied with slender 

 gripping teeth, indicate predaceous habits and in all probability a diet of fish or 

 cephalopods. 



In conclusion, I have to express my indebtedness to Dr C. W. Andrews for 

 providing me with every facility for studying the Leeds Collection at South 



