MESOSAURIA OF SOUTH AFRICA. 593 



tainty. On the right side are two bones a little displaced, which 

 may be the remainder of the right clavicle and the transverse bar 

 of the interclavicle. Both bones are wider than cervical ribs. There 

 is nothing to show whether the clavicular arch resembled that of Lario- 

 saurus and Nothosaurus, or that of Pareiasaurus and Anomodonts, 

 but that it existed seems probable. 



A pair of bony plates make the ventral part of the shoulder- 

 girdle, and cover much of the two succeeding vertebrae so that their 

 transverse processes are not seen. On both sides these bones are 

 fissured and broken by pressure. On the left side a suture extends 

 inward from near the acetabulum, which appears to have divided 

 the mass into a posterior coracoid part and an anterior scapular part. 

 On the right side the suture is not seen. There is a coracoid fora- 

 men, which is presumably in advance of the acetabulum. In some 

 Anomodonts the coracoid foramen is situate at the junction of the 

 scapula and precoracoid, in others at the meeting of the scapula, 

 coracoid, and precoracoid ; while it is entirely in the coracoid in 

 Crocodiles and Dinosaurs. Hence it may be inferred that the part 

 of the bone which thickens behind the foramen is the coracoid. 

 The thinner plate in front is the scapula. The part of the bone 

 which extends inward from the scapula towards the clavicle corre- 

 sponds to the precoracoid region, though there is no suture to define 

 it as a separate bone. The contour of the scapula is apparently not 

 unlike that of the Muschelkalk fossil Dactylosaurus gracilis, but the 

 coracoid is dissimilar.^ The correspondence is close with the 

 type Mesosaurus tenuidens. In that fossil the coracoids overlap, 

 while in this specimen they are separated, probably by post-mortem 

 pressure. On each side towards the median line there is a lunate 

 plate. Its inner border is convex, very thin, and apparently adapted 

 for squamous overlap. As it extends outward towards the coracoid 

 foramen it contracts. There is a deep semi-ovate emargination of 

 the posterior margin of the bone, external to which the posterior 

 border of the coracoid terminates in a transverse line. In front 

 of the emargination the bone thickens to an elevated band, which has 

 the aspect of connecting the lunate mass with the external part of 

 the coracoid and scapula, though there is no anterior emargination, 

 but only a depression in which the coracoid foramen is placed. The 

 external border of the scapula and coracoid is straight, with a 

 tendency to concavity behind the humeri, which extend transversely 

 outward from the middle of the border. In the impression from 

 the natural mould the anterior border of the scapula appears to be 

 rounded, but this may result from conditions of preservation. 



A thin plate of bone, of which the outlines are imperfectly defined, 

 extends laterally between the front of the scapula and the clavicle. 

 It appears to be continuous with the inner lunate mass which rests 

 on the 12th and 13th vertebrae, though it is not continuous with 

 the anterior border of the scapula, but above it. It is obviously 

 displaced, since the transverse process of the lOth vertebra extends 



^ Gurich, Zeitscbr. d. Deutsch. geol. Gresellsch. vol. xxxvi. (1884) p. 125, pi. ii. 



