22 Watson, New Genera of Upper Liassic Plesiosaurs. 



Blake gives a figure of a vertebra which, if really a 

 cervical, differs greatly from those of my animal ; it does, 

 however, present some slight resemblance to the more 

 anterior of the dorsals of the Manchester specimen. His 

 description states that the neural spines of the cervical 

 vertebrae lean back, so that their tips lie above the pos- 

 terior surface of the succeeding vertebrae, and thus agrees 

 with his figure. 



Blake states that in P. lotigirostris, 25 dorsal centra 

 fill a length of 80 in., giving at least 3 in. for the length of 

 an average dorsal centrum. None of my dorsals, which 

 represent all parts of the back, approach this length. 



In actual size and in relative length the pro-podials of 

 our specimen agree fairly closely with those of P, longi- 

 rostris, but the humerus has the anterior edge convex, 

 and not concave, as in the latter species. It is thus 

 impossible to refer our specimen to any known species. 

 It appears to be allied to the Longirostrate group of 

 Plesiosaurs, typically represented by P, rostratus, and also 

 including, y?^(? Lyddeker, P. longirost7'is. 



The vertebral column shows many points of resem- 

 blance to that of P. rostratus^ the cervical centra being 

 very similar, although relatively somewhat longer. They 

 also resemble those of " Thaumatosaurus" carinatus^ of the 

 Kimmeridge clay. 



The pro-podials are also very similar to those of 

 P. rostratus. 



Of the girdles of P. rostratus nothing is really known. 

 If Lyddeker is right in referring R. 1315 of the British 

 Museum to an allied species, it differed considerably 

 from ours in the pectoral arch. The clavicular arch of 

 our specimen presents many resemblances to that of 

 " Thaumatosaurus " arcuatus, although it differs in having 

 the posterior border convex instead of concave. 



