242 C. W. AndreiDs — On a Young Plesiosaur, 



The skull is comparatively short, the snout being blunt and 

 rounded ; its length is about one-third that of the neck. The 

 premaxill^, which are covered with irregular ridges, each bore 

 five or six slender teeth, the crowns of which are nearly smooth. 



The pineal foramen is large, and is situated between the anterior 

 ends of the parietals. These bones form a high crest between the 

 temporal foss£e, and posteriorly are produced outwards into short 

 processes which unite with the ascending rami of the triradiate 

 squamosals, the ventral rami of which unite closely with the 

 quadrate, while the anterior, wanting in this specimen, formed the 

 hinder portion of the temporal arcade. These squamosals are very 

 like the same elements in Sphenodon, and probably are equivalent to 

 squamosal + supratemporal . 



The basioccipital, which is still free from the basisphenoid, bears 

 the whole of the nearly hemispherical occipital condyle. The 

 basisphenoid is deeply excavated anteriorly by the pituitary fossa, 

 and has adherent to its ventral surface a plate of bone which is 

 prolonged anteriorly. This element, which must be regarded as 

 a para sphenoid, is well shown in some Pliosaur skulls in the British 

 Museum, in which it runs forward for some distance between the 

 pterygoids which unite with its outer edges. 



On the outer side of the exoccipitals, and when seen from the 

 outer surface of the skull, apparently arising from those elements, 

 are the large paroccipital processes which are directed outwards and 

 downwai'ds. If this region be examined on the internal surface, 

 it is seen that these processes spring from distinct elements (the 

 opisihotics) , still separated from the exoccipitals by deep clefts, 

 although externally the sutures are obliterated. The opisthotic 

 shows the impression of two of the semicircular canals. The supra- 

 occipital, which is very large, is also channelled b}'^ a portion of 

 the auditory labyrinth, there being no trace of a distinct epiotic 

 ossification. 



The mandible seems to have carried from 20 to 22 teeth; each 

 ramus is about 23 centimetres in length. 



The cervical vertebrae are 31 or 32 in number ; the neural arches 

 and cervical ribs are all free from the centra, a character depending 

 merely on the age of the individual ; the centra are short with oval 

 articular faces, which are much less concave than in the adult ; the 

 neural spines are short and stout, and the anterior and posterior 

 zygapophyses are respectively slightly concave and convex trans- 

 versely ; there is also a zygosphenal articulation. 



No union has yet taken place between the centrum of the axis 

 and that of the atlas (i.e. the odontoid) ; this latter bears the two 

 halves of the atlantal neural arch, which are widely separated from 

 the anterior wedge bone forming the lower fourth of the cup for 

 the reception of the occipital condyle. 



There are two or three pectoral and 21 or 22 dorsal vertebrae. 

 Behind these are three or four vertebree bearing short, somewhat 

 expanded ribs, which articulate between arch and centrum ; these 

 appear to be sacral. The caudals bear small rib-like chevrons, 



