THE ICHTHTOSATJEIA. 247 



postfrontal, inwards to unite with the parietal, and down- 

 wards to become connected with the pterygoid. A strong 

 and stout quadrate bone is connected with the exterior of 

 the skull, and presents a puUey-like surface to the articiilar 

 piece of the mandible. 



On the under- surface of the skull the long and slender 

 palatine bones are seen, bounding the posterior nares, which 

 are situated far forwards. Behind, and separated by an 

 interval traversed by the rostrum of the basisphenoid 

 bone, the very large pterygoids commence, by slender and 

 pointed ends, which lie on the inner side of the palatine 

 bones at the level of the posterior nares. They then widen, 

 and passing backwards with a slight outward curvature, 

 on each side of the sphenoidal rostrum, end in three pro- 

 cesses — one of which connects itself with the basisphenoid, 

 another passes outwards and backwards to the quadrate, 

 while the third runs upwards to the squamosal bone. 



The lower jaw is composed of two rami, which unite, 

 anteriorly, in a very long symphysis. Each ramus is com- 

 posed of the normal six pieces, the splenial being remark- 

 ably long, and entering extensively into the symphysis. 



We have no very clear knowledge of the structure of the 

 hyoidean apparatus in this reptile. 



The pectoral arch (Pig. 76, E) consists, upon each side, 

 of a narrow scapula (Sc), having the directieu usual in 

 Lacei-tilia, and a broad coracoid {Co.), the inner edge of 

 which does not overlap its feUow, but meets it throughout 

 in the middle line, as in Plesiosaurus ; so that, in this genus 

 also, the rhomboidal part of the sternum appears to have 

 been absent or very small. 



But there is a very distinct T-shaped interclavicle {LCI), 

 the backward prolongation of which is received between 

 the anterior ends of the coracoids, while its horizontal bar 

 is very closely united with the inner ends of two stout 

 cui-ved clavicles {CI.), the outer extremities of which abut 

 ao-ainst, and are no less closely connected with, the upper 

 part of the anterior edge of each scapula. This arrange- 

 ment of the clavicles and interclavicle presents interesting 



