246 PALEONTOLOGY. 



between the coracoids and pubicals. In the tail the heema- 

 pophyses are short and straight, and remain nn-united both 

 with the centrum above, and with each other below. The 

 tail is much shorter in the Plesio- than in the Ichthyosaurus. 



The skull is subdepressed ; its length is rather more than 

 thrice its breadth ; but the proportions somewhat vary in 

 different species. The cranial part, or that behind the orbits, 

 is quadrate ; thence it contracts laterally to near the maxillo- 

 premaxillary suture, where it commonly expands a little 

 before rounding into the obtuse anterior termination. 



The orbits are at or near the middle of the skull : estimat- 

 ing the length of this by that of the lower jaw, they are in 

 advance of the middle part in Plesiosaurus Hawkinsii. ~No 

 trace of sclerotic plates has yet been discerned in any specimen. 

 The temporal fossae are large subquadrate apertures. The 

 nostrils, which are a little in advance of the orbits, are scarcely 

 larger than the parietal foramen. Beneath them, upon the 

 palate, are two similar-sized apertures, the palatal nostrils. 



The lower jaw presents an angular, surangular, splenial, 

 and dentary element, in each ramus ; the dentary elements 

 being confluent at the expanded symphysis. There is no 

 vacuity between the angular and surangular or any other 

 element of the jaw. The coronoid process is developed, as in 

 Placoclus, from the surangular, but rises only a little higher 

 than in crocodiles. The alveoli are distinct cavities, and there 

 is a groove along their inner border in both jaws. 



When the successional teeth first project in that groove, 

 they give the appearance of a double row of teeth. All the 

 teeth are sharp-pointed, long, and slender, circular in cross 

 section, with fine longitudinal ridges on the enamel ; the 

 anterior teeth are the longest. 



The scapula is a strong triradiate bone, the longest ray 

 being formed by the acromial or clavicular process, which 

 arches forward and inward to abut against the sternum, or 



