88 REPORT — 1839. 



thyosaur may have been imbedded for traces of carbonaceousi 

 discoloration, or of an impression of this fin, from which some 

 idea might be formed of its shape and size*. 



Thus in the construction of the principal natatory organ of 

 the Ichthyosaurus we may trace, as in other parts of its struc- 

 ture, a combination of Mammalian, Saurian, and Ichthyic pe- 

 culiarities. In its great length and its gradual diminution we 

 perceive the Saurian character; its tegumentary nature, un- 

 supported by osseous rays, bespeaks its afl&nity to the Cetaceans ; 

 while its vertical position brings it close to the peculiar condi- 

 tion of the natatory organ in the Fish. 



But, it may be argued, the horizontality of the caudal fin of 

 the Cetacea is essentially connected with their exigencies as 

 breathers of the atmospheric air : without this means of dis- 

 placing a mass of water in the vertical direction, the head of the 

 whale could not have been brought with the required rapidity 

 and facility to the surface to inspire ; and as the Ichthyosaurus 

 was also an air-breather, a like position of the caudal fin might 

 be considered to be equally essential to its existence in the 

 water. 



To this objection it may be replied that the Ichthyosaurus, not 

 being warm-blooded, would not need to bring its head to the 

 surface so frequently, or perhaps so rapidly, as the Cetacean ; 

 and, moreover, a compensation for the absence of a horizontal 

 terminal fin is provided in the presence of the two posterior 

 extremities, which are modified as paddles, and which are wholly 

 deficient in the Cetacea. 



Thus I conceive that the living Ichthyosaurus must have pre- 

 sented the general external figure of a huge predatory abdominal 

 fish, with a longer tail and smaller caudal fin than usual ; scale- 

 less moreover, and covered, according to the minute and careful 

 observations of Dr. Buckland, with a smooth or finely- wrinkled 

 skin analogous to that of the Cetacea. 



A closer inspection of the enduring parts of these singular 

 inhabitants of the ancient deep, shows that under their fish-like 

 exterior was concealed an orgp-nization which, in the main, is a 

 modification of the Saurian type. 



Of the Cranium. — The general form of the cranium resem- 

 bles that of the dolphin, but it differs in the comparatively 



* I would more particularly recommend tWs observation to be made on spe- 

 cimens oi Ichthyosaurus from the lias of Barrow-on-Soar, whicb appears to have 

 been more favourable for the preservation of the soft integument than in other 

 localities. The specimen from which Dr. Buckland described the tegument of 

 the abdomen, and that in which the tegument of the fin and the soft rays were 

 described by uie, were both from Barrow-on-Soar. 



