PLESIOSAURIDJE. 



159 



with the intercarpal space generally flattened, and its ridges less 

 numerous than elsewhere. Keck short, with the anterior vertebrae 

 large. Cervical vertebrae with very short centra, bearing a strong 

 haemal ridge, with rugose external surface, and having elliptical or 

 circular and well-cupped terminal faces, and distinctly double 

 sessile costal facets ; and the arches either very short or mode- 

 rately elongated. Dorsal centra short. In the pectoral girdle 

 (when known) the scapulae resembling those of Plesiosaurus, but 

 the omosternum consisting of a large single plate, much expanded 

 transversely, with a wide and shallow anterior notch. In the pelvis 

 (when known) the ischium of the comparatively short type of 

 Plesiosaurus. Humerus longer or shorter than femur, and distally 

 articulating only with the radius and ulna, which are elongated and 

 separated by a considerable interval ; ulna and fibula more or less 

 reniform, and the femur in some cases longer than the latter. 

 Chevrons (if rightly determined) closed inferiorly. 



This genus was founded upon the evidence of imperfect teeth and 

 cervical and dorsal vertebrae from the Great Oolite of Wiirtemberg. 

 The cervical vertebrae show the deeply cupped and nearly circular 

 centra found in the so-called EhomaJeosaurus, and are quite distinct 

 from those of Pliosaurus, with which they have been said to be 

 identical l . 



Fig. 56. 



Thaumatosaurv* arcuatus. — Left lateral and posterior aspects of an anterior 

 cervical vertebra ; from the Lower Lias of Street, h. V^.z, prezygapo- 

 physis ; pt.z, postzygapophysis ; co, coital facets. The middle figure shows 

 the articulating surface of the postzygapophysis. 



Quart. Journ. Gcol. Soc. vol. xlv. p. 58 (188 ( J). 



