ROOM IV. ICHTHYOSAURUS LONCHIODON. 383 



specimens, is 1 foot in diameter, and the teeth 2J inches in 

 length. There is a scapula in the collection 17 inches long, 

 and 9 inches broad at the distal end ; and vertebra 6 inches 

 in transverse diameter. 



The teeth are distinguished from those of the other species 

 by the form of the crown, which is conical and subcompressed, 

 and has a sharp ridge on each side ; the base is not grooved as 

 in the teeth of I. communis : these dental characters suggested 

 the specific name. The numbers of the teeth are 4 ~ o . 



The head is relatively longer in proportion to the trunk 

 than in I. communis and I. intermedius. The lower jaw is 

 remarkably massive and powerful, and projects further back- 

 wards beyond the joint, than in the preceding species. 1 



Thevertebrse are about 120 in number; their bodies are 

 more compressed than in the other species. 



The anterior and posterior paddles are equal in size, more 

 simple in their structure, and composed of fewer bones, than 

 the extremities of the species previously described. This 

 structure, first pointed out by Mr. Hawkins, induced that 

 gentleman to name the species chiroligostinus (signifying few- 

 boned-paddle). 



The humerus is short in relation to its breadth : the femur 

 is proportionately longer than in other species. Professor 

 Owen remarks, that the small number of digital ossicles in the 

 extremities of this gigantic Ichthyosaurus, and the greater 

 distances at which they are placed from each other in the 

 lower half of the paddle, indicate " that the ligamentous sub- 

 stance which connected them together, entered more abun- 

 dantly into the composition of the fin." 



WALL-CASE D. [4.] 



Two exquisite skeletons of Ichthyosaurus communis. 

 (Hawkins, PI. XII.) 



Ichthyosaurus lonchiodon : a large specimen, comprising the cranium and jaws, the 

 vertebral column and ribs, and one of the anterior, and one of the posterior 

 extremities. 



1 " Brit. Assoc. Rep." 1839, p. 116. 



