XXX PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



In a second paper, read May 3, 1822, Mr. Conybeare was enabled 

 to describe much more fully all the relations of the genera Ichthyo- 

 saurus and Plesiosaurus, from the discovery of other remains, both 

 of the Ichthyosaurus and Plesiosaurus, by his coadjutor Sir Henry 

 Delabeche. A very minute examination of the teeth, especially, 

 enabled him to point out that those of the Ichthyosaurus were more 

 intimately related to the teeth of the Crocodile than to those of other 

 Lacertce (an opinion then at variance with the opinions of some ana- 

 tomists), whilst at the same time, in other respects, the analogy was 

 in the other direction, for Conybeare observes, " in pursuing, how- 

 ever, the history of the teeth of the Ichthyosaurus to the last stage, 

 we quit these analogies with the Crocodile, and arrive at another 

 point wherein the Ichthyosaurus resembles the other Lacertm, in com- 

 mon with many of the Mammalia : this is, the gradual obliteration of 

 the interior cavity in old age, by the ossification of the pulpy nucleus." 

 In conjunction with Sir H. Delabeche he brought up the number of 

 species to four, determined from the teeth ; and in his further con- 

 sideration of the genus it is right to notice the following remarks, 

 proceeding from him after noticing a difference in one character of 

 the fossil Crocodile, when compared with the recent, as stated by 

 Cuvier : — " I am persuaded, from every circumstance, that a much 

 nearer approximation to the structure of the older lacertian genera 

 will be found in the fossil than in the recent Crocodiles ; interesting 

 links in the chain of Saurian animals will be thus supplied, and it 

 will probably be found that many of the points in which the Ich- 

 thyosaurus differs from the recent type are only instances of its 

 agreement with the fossil." 



The researches of Sir H. Delabeche had not at this time led to the 

 discovery of a complete skeleton of the new genus Plesiosaurus ; but 

 additional portions of it were found, including a very perfect dental 

 bone of the lower jaw, whilst a tolerably perfect head was discovered 

 by Mr. Thomas Clarke in the Lias of Street, near Glastonbury. 



The investigation of these new relics of the Plesiosaurus led Mr. 

 Conybeare to the following conclusion : " On the whole then, the 

 manner in which the ribs of the Plesiosaurus articulate throughout, 

 by a single head, to the extremity of the transverse processes of the 

 vertebrae only, the structure of the humero-sternal parts, and the 

 characters derived from the head, approximate this animal most nearly 

 to the Lacertce. By its teeth, on the other hand, it is allied to the 

 Crocodile ; while its small nostrils and multarticulate paddles are 

 features in which it resembles the Ichthyosaurus" This able paper 

 he concluded with words characteristic of his natural modesty, after 

 pointing out the difficulty of rendering anatomical details at once sci- 

 entifically accurate and yet attractive to a general audience : " I need 

 not add how much these difficulties will be increased in the hands of 

 a writer who must acknowledge that, while intruding on the pro- 

 vince of the comparative anatomist, he stands on foreign ground, and, 

 using almost a foreign language, is frequently driven to adopt an 

 awkward periphrasis, where a single word from the pen of a master 

 would probably have been sufficient." 



