﻿LIASSIC FORMATIONS. 



11 



a broad and short muzzle, of an equilateral triangular figure if the transverse lines 

 across the fore part of the orbits be taken as the base, the two sides converging to the 

 rounded apex in almost straight lines, with a feeble indication of a constriction where 

 the maxillo-prcniaxillary suture seems to be. The contour is undulated by the expan- 

 sions for the sockets of the larger teeth, which produce risings, with intervening 

 furrows on the granulate alveolar borders of the jaws. The mandibular rami 

 converge to their terminations at the symphysis, which is not prolonged or expanded. 



The specimen (Tab. Ill, fig. 1) from the Lias of Charmouth was wrought out 

 of its matrix by the estimable discoverer of the Liassic Dinosaur (Scelidosaurus) 

 described in a former Monograph. It is an admirable example of patience, pains, and 

 skill; in the bestowal of which, for the furtherance of science, upon the fossils roughly 

 wrought out of the quarries in his neighbourhood, Mr. Harrison found solace during 

 the long and trying illness which confined him to his bed, until his final release by 

 death. 



Pectoral and pelvic limbs (Tab. I, figs. 2, 3). 



To complete the characters of Plesiosaurits dolichodeirus I have reproduced, in out- 

 line, the bones of the pectoral, fig. 2, and pelvic, fig. 3, limbs, as they are preserved in 

 the type-specimen. The humerus, $3, shows rather more convexity at the anterior 

 border, and a deeper concavity at the posterior border than in some other species 

 (Plesiosaurus HawHnsii, PI. macrocep/talus* PI. rugosus, e. g.). The radius, 54, and 

 ulna, 55, are of equal length ; the ulna not being shorter than the radius, as in PL 

 Hawhnsii (Tab. XIV, fig. 6) ; the ulna has not the olecranal process or epiphysis, as 

 in the PI. rugosus (Tab. XIV, fig. 2, 55') ; and both antebrachial bones are less broad, 

 in proportion to their length, than in the PI. macro c ep hal '// : s f (Tab. XIV, fig. 4). The 

 carpus shows seven bones, four in the proximal, three in the distal row ; their homo- 

 logies will be pointed out in the description of Plesiosaurus rugosus. The metacarpal 

 of the first digit (Tab. I, fig- 2, i), answering to "pollex," supports at least three 

 phalanges ; that of the fifth digit, seven phalanges ; the metacarpal of each of the 

 others, six phalanges, but the terminal ones may be wanting in some. The pelvic 

 fin (fig. 3) is rather longer than the pectoral one ; in both fins the fifth digit (v) 

 articulates on a more proximal plane than the others, i. e. nearer the trunk, as in most 

 other Plesiosauri. In the same skeleton the pectoral limb equals seventeen of the 

 middle cervical vertebrae in length ; % in PI. macrocep/ialus it equals sixteen of these 

 vertebras, in PI. rugosus it equals fifteen. 



* ' Geological Transactions,' 2nd series, vol. v, pi. 43. 

 f lb. 



% The artist has drawn the outline of the limb-bones, figs. 2 and 3, on a larger scale than that of the 

 skeleton, in Tab. I. 



