476 PROP. "W. J. SOLLAS ON PLESIOSATJRTTS 



Fig. 13. — Transverse Section through the Jaws e>/P. megacephahis. 



(Scale J.) 



Ann 



T, tooth. 



vertebrae can only be indirectly arrived at. The total length of 

 that part of the vertebral column which lies between the anterior 

 edge of the furculum and the posterior edge of the ischium is 

 70 inches ; from this 2-3 inches must be deducted on account 

 of the concealed last cervical vertebra, and 6*9 inches for three post- 

 dorsal vertebrae supposed to be concealed beneath the ischium, two 

 of them being sacral and one the first caudal. This leaves 60*8 

 inches (70-2-3 — 6*9 = 60-8), which is the length of the dorsal 

 region. Divided by 2*3, the average length of a dorsal vertebra, this 

 gives 26-43, or, neglecting the fraction, 26, which is the number 

 of vertebrae in the dorsal series. These numbers are embodied 

 in the annexed Table (page 477), in which the measurements of a 

 number of specimens of different species are compared together. 



PlesiosatjPvTjs brachycephaltjs, Owen. (Plate XXIV. fig. 2.) 



This species has not been figured, and has been only partly described. 

 I do not intend here to do more than offer a few observations upon it, 

 and to correct the previously made measurements. 



1. The Skull. — Although incomplete and broken, the skull is but 

 slightly distorted, and presents several points of interest. 



The snout is broken away from the rest of the skull, and shows 

 the under surface perfectly. It is 5 inches long, and does not 

 exhibit the internal nares ; so that they must have been situated 

 further back. Its broken surface extends at right angles to its long 



