104 The Rev. ^V. D. Cdnybeaue's Additional Notices 



the back of the mouth and head ; an attempt to discriminate the species of this 

 genus ; and a fuller statement of the analogies which must determine its place 

 among the ditVerent classes of lacertse. I had originally, it will be remem- 

 bered, compared it principally to the crocodile ; and after a very mature exa- 

 mination, I am still of opinion that the analogies between the Ichthyosaurus 

 and that family are more striking and numerous, than those which connect it 

 with the other tribes of Lacertae. But to judge of the relative value of con- 

 flicting analogies is one of the most delicate and difficult points of compara- 

 tive anatomy ; and I shall throughout confine myself to stating simply those 

 analogies, whatever may be their tendency, leaving those who may be more 

 competent to such a task, to decide on the conclusions to be deduced from 

 the whole evidence*. 



I need not repeat, what is fully agreed on all hands, that the Ichthyosaurus 

 is an animal entirely sui generis ; possessing, however, sufficient analogies 

 with the Saurian order to justify our referring it to that great natural division. 

 It is likewise agreed, that in respect of certain analogies, it is allied most nearly 

 to the crocodilian branch, and in respect of others to the lacertian branch of 

 that order : and the remaining question, to which of these it approximates 

 most nearly, is one, after all, of very subordinate importance. Concerning 

 this most material point, viz. that the animal was exclusively an inhabitant of 

 the sea, no doubt has been expressed by any of those who have most atten- 

 tively considered its structure. 



It is very satisfactory to me to be able to state, that the progress of my 

 inquiries, though it has affiarded clearer views on many points, has scarcely 

 in any material circumstance obliged me to alter those which I have had the 

 honour of laying before the Society on a former occasion. Some slight modi- 

 fications will be found in the course of the following observations ; but there 

 are only two points which appear to require a more prominent notice ; — 



* It cannot be too often pressed on the zoological observer, that he must carefully keep in view 

 the collective tendency of all the analogies presented by the subject before him : in no depart- 

 ment of inquiry are we more liable to fall into error from hasty induction. To instance this in 

 a recent animal, the Ophisaurus : Mere the head alone of this animal known, no person ac. 

 quainted with comparative anatomy would hesitate to pronounce that it belonged to a Lacerta, 

 and was connected with a body having regular quadrupedal extremities ; yet in truth its body 

 belongs to an entirely different system, being that of a regular Serpent. In the same manner in 

 the fossil genus Ichthyosaurus, the head of a lacertian animal is joined to the vertebrae of a fish 

 and extremities entirely sui generis. Beautiful as is the doctrine of the laws of coexistence in 

 the parts of animals, so admirably illustrated by Mr, Cuvier, it yet requires to be applied with all 

 the caution so conspicuous in the writings of this naturalist, to render it a secure instrument of 

 investigation. 



