f,20 WILLI AM R. SMELLTE ON 



The figures (text-fig. 7, A and B) and measurements of the shoulder-girdle show 

 some of the points of difference between this species and Cryptocleidus oxoniensis. 

 Notable points of difference are seen in the relative proportions of the shoulder- 

 girdle, Api'ac/oclcidus being much shorter and relatively broader; processes are 

 longer, ossification is much more advanced, and the mid-ventral portion of the girdle 

 is carinate between the coraco-scapular fenestra. The increase in the ventral ramus 

 of the scapula has brought it forward till it forms the anterior end of the shoulder- 

 girdle, leaving the retracted clavicle lying functionless behind the upturned tip. In 

 the scapula the angle between the glenoid surface and the surface of union with the 

 coracoid is 110 degrees, as compared with 90 degrees in Cryptocleidus. This change 

 better enables the glenoid to receive a more directly forward thrust from the head 

 of the humerus at each drive of the paddle, and this makes for increased speed. It 

 is uncertain whether the shoulder-girdle contained an interclavicle or not. The 

 clavicle is obscurely notched on the median margin about a third of its length from 

 the forward end, so that it is possible that a rudimentary interclavicle may have 

 been present and either lost or never ossified. 



The bones of the fore limb are in a very perfect state, have suffered no crushing 

 or distortion, and exhibit details of articulation and muscle attachment as clearly as 

 freshly macerated bones. Comparison of the figures (text-fig. 8, A, B, C) shows the 

 striking manner in which the fore limb combines the characteristics of Tricleidus 

 and Cryptocleidus. The humerus (B, hum.) is very similar to that of Cryptocleidus 

 (C, hum.), but can be easily distinguished from it by the facets on the distal end. 

 The head (h.) is almost circular in outline, and bears a convex roughened surface ; 

 the convexity and roughness are greatest in the centre, while the rim at the circum- 

 ference is comparatively flat and smooth. The edge is sharp and cleanly cut, and the 

 state of the whole head is such that the cartilage cap might have been removed 

 only recently. The surface of the head is continued across a narrow (3 cm.) 

 concave passage into that of the tuberosity (tu.) which forms an irregular quadrate 

 prominence situated on the outside of the head and slightly to the posterior. The 

 tuberosity has also been capped with cartilage, but it is convex only near the outside 

 and is deeply concave between that and its junction with the head of the humerus. 

 The prominent anterior and posterior borders of the tuberosity are soon lost amid 

 the deep rugosities (m.r.) which cover the outside of the upper surface, and shade 

 inconspicuously into the general contour of the oval neck; The short, strong shaft 

 of the bone appears slender by comparison with the massive head and wide distal 

 expansion. Both margins are concave, the posterior being more so. The rugosities 

 on the posterior margin of the great tuberosity are continued to the posterior border 

 and inner side of the shaft, where they become very pronounced. The anterior 

 margin is sharply rounded and smooth except for a few rugosities on the upper part 

 of the shaft which are a continuation of those on the anterior of the great tuberosity. 

 The distal expansion is very wide (24'6 cm.), but only 4 cm. deep at its thickest. It 



