466 PROF. W. J. SOLLAS OS A NEW SPECIES OF PLESIOSAUEUS 



Ilium. 



Eight ilium. Left ilium. 



inches. inches. 



„ distal (d d) 



Minimum diameter of shaft (m m) 



Length (J J, fig. 7) 



Breadth of proximal end {p p) 



6-9 7'2 

 2-4 (?) 2-85 

 2-3 1-9 



10 



Note.— The proximal end of the right ilium is slightly broken, and its distal 

 end compressed, probably by subsequent pressure. 



These bones, which are smaller than the humeri, have the arti- 

 cular head well denned by a sharp surrounding ridge ; the articular 

 surface itself is deeply pitted and tuberous, indicating the previous 

 existence of a thick covering of cartilage which has since dis- 

 appeared. 



The cylindrical proximal end is slightly constricted below the 

 capitular ridge before it begins to expand. The dorsal and ven- 

 tral margins are almost straight lines, or only slightly concave 

 curves, which diverge gently from the thick proximal to the broad 

 and flattened distal end. The distal end is truncated by a simple 

 gently convex curve. 



The surface of the bone is roughened beneath the head, and 

 strongly ridged at the distal end with - longitudinal lines, which 

 diverge in conformity with the curves of the lateral margins of 

 the bone. 



Kemains of what appears to be some dermal structure have been 

 stated by previous writers to occur in connexion with Ichthyosaurus ; 

 and Charles Moore in particular has well described a thin layer 

 having a wrinkled surface, which invests a large number of the 

 Ichthyosaurs in the collection of the Bath Museum ; but no one, so 

 far as I know, has made mention of any similar investment in the 

 case of Plesiosaurus. Great interest therefore attaches to the 

 presence of a thin brownish film, with characteristic surface-mark- 

 ings, which coats a considerable portion of the specimen under con- 

 sideration. 



It is best displayed on the surface between the fortieth and 

 sixtieth vertebras, covering the bodies, transverse processes, and 

 neural spines of the vertebras, the ribs, and the surface of stonj- 

 matrix intervening between them. It also extends in a band over 

 an inch broad, along the distal ends of the neural spines, at a little 

 distance from them as now exposed. 



This band, which seems to restore the dorsal outline, ends in the 

 pelvic region, where it covers the head of the right femur, and 

 imbeds a small oblong bone, the smooth shining surface of which 

 is raised into three parallel longitudinal ridges ; other fragments of 



The Femora. 



The Integuments. 



