AN ICHTHTOSATTETJS PEOM THE LIAS OP WHITBY. 643 



a posterior compressed mass from which a process extends, at first 

 outward and then backward and somewhat downward, lapping 

 along the inner side of the quadrate bone. The external lateral 

 concavities narrow the width of the pterygoid bones, and where 

 they terminate anteriorly the bones widen again, but begin to con- 

 verge forward and inward, terminating in sharp points. Their 

 surfaces are smooth, and slightly convex from side to side in 

 front. They descend a little downward as they extend outward, and 

 are moderately thick bones. The length from the process meeting the 

 quadrate to the anterior termination is about 13 inches on the 

 right side, but apparently rather more on the left side. The least 

 width from side to side between the external concave lateral 

 margins in the hinder part of the bone is about 5| inches. The 

 greatest width between the quadrate bones is nearly 10 inches. The 

 width at the angle where the lateral concavity terminates in front 

 is, across the bones and their interspace, less than 7 J inches. The 

 least width of each bone in its posterior constriction is rather over 

 an inch and a quarter. Its width at the expansion in front of the 

 constriction is over two inches. The distance from the posterior 

 quadrate process to the anterior termination of the lateral concavity 

 does not exceed 7| inches. 



Lying within the pterygoid bones, and joining them by sutures 

 nearly parallel to each other, are two bones which are to be regarded as 

 vomers (y). They prolong the tapering outlines of the pterygoid bones 

 inward, forward, and upward into the palate. They are divided from 

 each other by the presphenoid bone. That on the left side extends 

 somewhat further back than the bone on the right side. The least 

 distance from the hindermost termination of the bone on the left side 

 to the occipital condyle is about 10 inches, but about 4| inches fur- 

 ther forward the condition of the specimen becomes a little obscure 

 owing to a fracture here : there appear to be on each side of the pre- 

 sphenoid two small palatal vacuities, that on the right side being the 

 larger and a little over an inch long. It is uncertain therefore 

 whether these bones terminate at this point. If so, they can only 

 be an anterior dismemberment of the pterygoids, and probably a 

 distinct generic character in this Ichthyosaurian type. But in front of 

 these perforations median palatal bones of corresponding width are 

 prolonged forward in continuation of them, and without any appear- 

 ance of break: and as I have found the vomerine bones lying on the 

 sides of the anterior termination of the presphenoid in some transverse 

 sections of small Ichthyosaurian skulls from the Lias, I am inclined 

 to believe that the parts posterior to the perforations, as well as the 

 long anterior bar or bars, are vomers. The vomers would appear to 

 reach forward, in front of the small perforations referred to, to the 

 extremity of the palate as preserved ; but the condition of the palate 

 does not demonstrate in this species whether the forward and narrow 

 prolongation consists of two distinct bones ; but on the polished end 

 of the broken snout the two bones are visible in front (fig. 4). 



External to the pterygoid bones, and equally prolonging the 

 lateral contour, is another pair of slender bones which do not reach 



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