and Clavicular Arch in Sauropterygia. 123 



sented on the scapular side of the foramen in all members of that 

 class except the Ornithosauria. Its individuality is retained in some 

 of the Sauromorpha; and, although they have no distinct osseous 

 representative of the bone, the nearest analogy to the shoulder girdle 

 in Sauropterygia is found among Nothosauria ; and there is no doubt 

 that these resemblances and those with Anomodonts are closer than 

 with existing orders of animals. 



The Nothosaurian shoulder girdle contains the same number of 

 constituent elements as in Sauropterygians, and the same nomencla- 

 ture has been applied to them. There are some slight differences in 

 the coracoid. In the ISTothosauria it lies more obviously behind the 

 glenoid cavity, while in many Plesiosaurs, especially the typical forms 

 from the Lias, it also has a considerable median anterior extension. 

 Further, in Nothosaurs there is a notch in the anterior margin of 

 the coracoid, already contrasted with the similar notch in the coracoid 

 of Ichthyosaurs, anterior to which are rough cartilaginous surfaces of 

 scapula and coracoid, which have the aspect of having supported a 

 cartilage which completed the coracoid foramen. There is no anterior 

 prolongation of the scapula in Nothosaurus such as is seen in Plesio- 

 saurus, but the clavicles are much elongated. They form a squamous 

 overlap on the visceral surface of the scapula, according to von 

 Meyer, and their length, and prolongation forward, removes the 

 interclavicle from contact with the coracoids. If the suggested pre- 

 coracoid cartilage in Nothosaurus existed, it makes the nature of 

 both coracoid and scapula clearer in Plesiosaurus, and shows that the 

 precoracoid need not be displaced into the position here assigned to 

 the clavicle. 



First, the foramen which appears to be indicated in the anterior 

 margin of the coracoid in some species of Ichthyosaurus as a deep 

 narrow notch, in other species widens to a concave anterior border to 

 the bone ; and similarly, in the specimen figured by Deecke as Lario- 

 saurus Balsami, there is no trace of the anterior notch in the coracoid 

 such as characterises Nothosaurus, but that bone has a smooth sharp 

 anterior concave border such as the bone shows in Plesiosaurus. It 

 would therefore seem to follow that the precoracoid foramen of Notho- 

 saurus becomes the coraco-scapular foramen of Plesiosaurus, and that 

 the precoracoid in Elasmosaurs ceases to exist as a distinct cartilage. 

 It cannot be inferred to be lost by connation with the coracoid, because 

 the foramen might then be supposed to persist, but, as there is no 

 foramen in either the scapula or coracoid,* there is no evidence of the 

 composite nature of either bone in Plesiosaurus. Nevertheless, since the 

 precoracoids meet in the median line in many Amphibians, and in 

 Chelonians, and the scapulae never have a median ventral union, there 

 is an a priori probability that bones formed from cartilage, placed 

 * Always subject to the doubtful evidence of the Brit. Mus. fossil 2041*. 



