294 DR. C. W. ANDREWS ON A NEW PLESIOSAUR [vol. IxXTiii, 



is more marked. There is a trace of the anterior border of a fora- 

 men in the posterior prolongation, most of which however has 

 been broken away. The clavicles (c/.) interlock with the inter- 

 clavicle in a complex overlapping suture (see Seeley's figure). 

 Posteriorly they are crushed and incomplete, and so it cannot be 

 seen whether they met in the middle line or extended back to over- 

 lap the coracoids. In the very similar but more complete clavicular 

 arch ascribed by Lydekker to Thaumatoscmrus megaceplialus^ 

 and referred to above, the posterior portions of the clavicle and 

 interclavicle are much more complete (text-fig. A, p. 295). Here it 

 can be seen that the interclavicle (i.cl.) is prolonged backwards 

 into a bifm'cated process, enclosing a foramen or notch (for.). 

 The clavicles (cl.) overlap on to the ventral face of this prolon- 

 gation, and appear to meet below it in the middle line, extending 

 behind it. If the coracoids in this Plesiosaur were similar to those 

 of P. arcuatus, the clavicles must have overlapped the upper surface 

 of their anterior prolongations, thus enclosing a fenestra as in the 

 specimen here described. 



The scapula in P. arcuatus is generally similar in form and in 

 its relation to the clavicular arch, but differs in details from the 

 Wealden specimen : the ascending ramus is much stouter, and 

 widens instead of narrowing towards its upper end, which is 

 occupied by a surface for a supra-scapular cartilage. The anterior 

 portion of the ventral ramus does not widen out to the same 

 extent; its inner face against which the clavicle fits is gently 

 curved, and slopes downwards instead of forming a sharply angu- 

 lated shelf. The coracoids of P. arcuatus differ in having their 

 anterior prolongations much broader and shorter. Behind the 

 thickened symphysial surface in the interglenoid region the median 

 borders of the coracoids, instead of having their sharp edges 

 separated by a considerable interval, were fringed with cartilages 

 which must have met in the middle line. In Brancasamnts also 

 they are separated for a considerable distance behind the symphysis, 

 but unite posteriorly at the postero-internal angles. 



Lydekker has referred both the reptiles originally described as 

 JPlesiosaurics arcuatus and P. megacejjlialus, to H. von Meyer's 

 genus Thaumatosaurus, without any apparent justification. This 

 genus was founded on some imperfect dorsal and cervical centra, 

 some fragments of jaw with broken teeth, and some pieces of rib 

 from the Grreat Oolite of Wiirtemberg. Nothing is known of the 

 structure oi: the skull, shoulder-girdle, or pelvis ; and it is 

 exceedingly improbable that the Lower Liassic species above men- 

 tioned are referable to it. It seems better, therefore, that those 

 Liassic species possessing the type of shoulder-girdle described 

 above, as also a double costal facet on the cervical vertebrae in the 

 centra of which there is no sharply-defined central concavity, 

 should be referred to a new genus, for which the name Eury- 

 cleidus may be suggested, the type species being E. arcuatus. 



1 See Cat. Foss. Eept. Brit. Mus. pt. ii (1889) p. 167. 



