Manchester Memoirs, Vol. liv. (1909), No. 4. 25 



The shape of the clavicle reminds one of Microckidus, 

 particularly in the way in which the lateral angle fits into the 

 anterior ramus of ihe scapula. So far as I know, in all 

 Plesiosaurs except such Elasmosaurids as Microcleidus and 

 Cryptocleidus., the whole clavicular arch is fused into one solid 

 bone, and Dames' suggestion of an open suture in the clavicular 

 arch of P. Guiklmi Imperatoris confirms me in the idea 

 that it is on the way to become an Elasmosaurid, or more 

 probably has separated from a stock some members of which 

 will become Elasmosaurians. 



The pubis of Dames' species is similar to that of the York 

 skeleton of Microcleidus homalospondylus. 



A specimen in the Manchester Museum which shews 

 cervical, dorsal, sacral and caudal vertebrae, a pubis, femur, 

 and some other bones of the hind leg, resembles P. 

 Guiklmi Iviperatoris, in having somewhat shorter cervicals than 

 Microcleidus hofiialospofidylus, and in their having rather longer 

 spines. I have regarded this specimen as representing an un- 

 described species of Microcleidus, but it is possibly identical with 

 the German species. 



This latter species appears to me to have some genetic con- 

 nection with Alicrocleidiis ; it is probably a conservative branch 

 from the Microcleidus stock which separated off after the high 

 dorsal neural spines had been acquired, but before the elongated 

 cervicals and Elasmosaurid arch were developed. 



I do not think that it ought to be included in Plesiosaurus 

 S.S., for it is undoubtedly very different from such species as P. 

 dolichodeirus and P. Haivkinsi. 



It cannot be included in Microcleidus, because that genus is 

 intended to include Plesiosaurs in this line of descent which are 

 sufficiently advanced to have the scapulae meeting in the middle 

 line. It therefore should have a new genus founded for it. I 

 refrain from suggesting a name until I have seen the specimen. 



The set of caudal vertebrae figured in the same paper as P. 

 suevicus, resemble fairly closely the anterior caudals of J/. 

 homalospondylus . Many plesiosaur caudals are much alike, but 



