on the Fossil Genera Ichlhj/osaurus and Plesiosaurus. J 23 



1 shall conclude these details by noticing a series of vertebra discovered 

 in the Kimmeridg-e clay near Weymouth, and exactly corresponding to spe- 

 cimens found in the same formation in Headington pits near Oxford. They 

 appear to belong to a species of plesiosaurus, as will be seen by comparing 

 them with the vertebrae figured in the former memoir. There is this great 

 difference, however ; that in the plesiosaurus of the lias, the length of the 

 side in the cervical vertebras is greater than in the dorsal ; in these the pro- 

 portions are reversed : the latter are figured in Plate XXII. fig, 4 to K, and 

 may be thus compared with the series before given in Vol. V. — 



Fig. 4, Plate XXII. of the pre- 1 



"^ ' . ,. ^ \ with fig. 4 & 5, Plate 41, Vol. V. 

 sent communication ) ° ' ' 



Fig. 5 with fig. 6 



Fig. 6 with fig. 7 



Fig. 8. will be found exactly to resemble the ordinary form of the middle 

 dorsal vertebrae in the plesiosaurus. 



These vertebrse are more than three inches in diameter, yet the annular 

 part has not anchylosed to the body. 



I cannot conclude these observations without appealing to the reader's in- 

 dulgence, as well on account of the nature of the subject, as of my own 

 inexperience in the branch of science to which it relates. To the observer — 

 actually engaged in tracing the various links that bind together the chain of 

 organized beings, and struck at every instant by the development of the most 

 beautiful analogies, almost every detail of comparative anatomy, however 

 minute, acquires an interest, and even a charm ; since he is continually pre- 

 sented with fresh proof of the great general law, which Scarpa himself, one 

 of its most able investigators, has so elegantly expressed — " Usque adeo Na- 

 tura, una eadem semper atque multiplex, disparibus etiam formis effectus 

 pares, admirahili quddam variciahnn shnpUcitate conciliat:" — Yet when these 

 very details are reduced to the technicalities of language, and when a perpe- 

 tual struggle against the difficulty of conveying clear ideas of the relations of 

 form through the medium of words, is to be sustained, they must often unavoid- 

 ably appear dry and tedious. I need not add how much these difficulties will 

 be increased in the hands of a writer, who must acknowledge that, while in- 

 truding on the province 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. 



R 2 



