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FOSSIL REPTILIA OF THE 



Plesiosaurus rugosus, Owen. Tabs. XIV and XV. 



This species, originally indicated by characters of detached vertebrae,* has received 

 ample elucidation from the fine specimen (Tab. XIV) presented by His Grace the 

 Duke of Rutland, K.G., to the British Museum. It was obtained from the zone of 

 Lower Lias of Leicestershire, characterised by the Ammonites stellaris, in the neigh- 

 bourhood of Granby. 



This specimen of the Plesiosaurus rugosus presents a similar condition to that of the 

 PL dolichodeirus decribed by Conybeare,f save that the head is not preserved in 

 advance of the small, scattered vertebrae of the anterior part of the neck ; about 

 five-and-twenty vertebrae of this region preserve their consecutive arrangement, most 

 of them in almost a straight line. The vertebrae of the trunk have suffered a greater 

 degree of dislocation, and, the specimen having been exposed in a prone position, they 

 are so dispersed as to permit to be seen the upper or inner surface of the coracoids, 

 the abdominal ribs, and the pubic and ischial bones. Two thirds of the caudal 

 vertebrae show the same scattered and dislocated condition ; but nine near the end of 

 the tail have preserved their natural position, as consecutively articulated, and appa- 

 rently their true relative position to the trunk. The four paddles are preserved 

 outstretched, as naturally articulating with their respective arches of support, with the 

 superior or external surface of the bony framework exposed. 



The cervical vertebrae, which have retained their natural consecutive arrangement 

 and juxtaposition, have undergone the same partial rotation as is observable in most 

 Plesiosaurian skeletons from Liassic beds, presenting their broadest surface or sides to 

 view ; the neural spines have here rotated toward the left side. Besides the twenty- 

 five cervical vertebrae which are more or less consecutive, three or four are huddled 

 in a heap at the base of the neck, and five or six are scattered at its fore part. From 

 the size of the articular surface of the foremost of these, which measures but six lines 

 in diameter, as well as from so much of the length of the neck as is demonstrated, it 

 may be inferred that the head was small, as in the PL dolichodeirus. 



Cervical vertebra (Tab. XV). 



One of these vertebrae, corresponding in position to the fifteenth cervical of the 

 PL rostratus (Tab. X), was carefully wrought out of the matrix of the specimen 

 Tab. XIV, and is represented of the natural size in Tab. XV. Its proportions show 

 that the present species, like PL dolichodeirus and PL Hawkimii, belongs to the section 



* ' Report on British Fossil Reptiles,' 1839 ; ' Reports of the British Association,' 8vo, 1840, p. 82. 

 t Tout), cit. 



