BRITISH FOSSIL REPTILES. 109 



appears to be bounded by a straight line above and a curved one 

 below. The upper maxillary bone receives the anterior part of 

 the malar bone in a notch ; and the slender, elongated malar 

 forms the whole inferior boundary of the orbit. 



The parietal transverse processes are excavated posteriorly 

 for muscular insertions. 



The extent of the symphysis of the lower jaw is nine inches, 

 where the whole length of the jaw is two feet nine inches. 



The surangular bone is perforated by a small foramen. 



At the posterior part of the jaws the teeth diminish in size as 

 they are situated further back. In the large head in Lord Cole's 

 museum the longest tooth presents an exserted crown of two 

 inches in length, and seven lines diameter at the base. 



The surface of the cranial bones presents a silky appearance, 

 owing to the fine striae with which it is impressed. 



The vertebra are in slight degree more compressed in the an- 

 tero -posterior direction than in the Ich. intermedins. I count 

 forty vertebrae between the occiput and that which from its re- 

 lative position to the iliac bones might be regarded as the sacral 

 vertebra; from this to the extremity of the tail I have found 

 100 vertebrae ; in all 140 vertebrae. 



The humerus is shorter and stouter in proportion to its length 

 than in any other species of the genus. The fore paddle is re- 

 latively broader than in the Ich. intermedins, and appears to have 

 an additional series of digital bones. The component phalanges 

 are transversely oblong ; the larger ones are hexagonal or penta- 

 gonal, with the angles more or less rounded off; they become 

 more rounded as they diminish in size towards the extremity of 

 the digital series. I cannot perceive that distinction in the form 

 of the phalanges of the Ich. communis as compared with those 

 of the Ich. intermedins which led Mr. Hawkins to designate the 

 latter cheiro-paramekostinus or oblong-boned. Neither does the 

 pointed form of the paddles peculiarly characterize the Ich. 

 communis. 



After a careful comparison of the most perfect specimens of 

 the anterior paddles of the two species, Ich. communis and in- 

 termedins, I am disposed to consider that the Ich. communis 

 has an additional digital series, and about fifty additional pha- 

 langial ossicles, increasing upon the whole the breadth and 

 power of the anterior fins. This increase in the strength of the 

 powerful locomotive members accords with the more robust 

 character of the head and teeth. 



I am unable to fix upon any one useful distinguishing cha- 

 racter in the hind paddle, between the Ich. communis and in- 

 termedins. 



They resemble each other more closely in the structure of 



