of the Order Enalio Sauri (o/"Conybeare). Ill 



In order to demonstrate wherein the present differs from 

 those species of the Ichthyosaurus already described, it will 

 be necessary briefly to state their specific characters, which, as 

 in most other instances, have been drawn principally from the 

 teeth. 



1. 1. communis. Upper part of the tooth conical, not very 

 acute, slightly aduncate, and thickly covered with prominent, 

 longitudinal striae. 



2. /. platgodon. Upper part of the tooth smooth and flat- 

 tened, so as to present sharpened edges. 



3. /. tenuirostris. Teeth more slender than the preceding 

 species, but is best marked by the extreme length and thinness 

 of the snout. 



4. I. intermedins. The upper part of the teeth much more 

 acutely conical than in species first ; and the striae less pro- 

 minent, yet less slender than in species third. These species 

 vary in size : those of the first differ from five to fifteen feet, 

 but the most gigantic belong to species second. 



The animal to which our specimen belonged may have been 

 about six or eight feet in length. The remnant from which 

 these observations were drawn is a portion of the dental bone 

 of the right side ; its greatest length four inches, greatest 

 breadth two inches ; alveolar surface three inches and a half 

 long, three-tenths in thickness. 



" The most important difference between the lower jaw of 

 the Crocodile and Ichthyosaurus is, that the bones are not 

 connected by true suture in the latter, but by squamous suture 

 as in fishes*." 



In which circumstance our specimen perfectly corresponds, 

 as is demonstrated by fig. 4. (a.) The inferior and posterior 

 edges being thinned and imbricated for articulation with the 

 angular bone. 



There are eighteen teeth in different states of preservation ; 

 the longest are°seven- tenths of an inch, two-tenths only pro- 

 jecting above the bone; the projecting part enamelled, smooth 

 "and shining, lanciform; the edges very sharp : but this will 

 be better understood by referring to fig. 1st. The bodies of 

 the teeth are all hollow, and are firmly fixed in a longitudinal 

 groove, there being no distinct, separate alveola?. The bodies 

 of the teeth are in close contact throughout, in which respect it 

 differs from the other species of the Ichthyosaurus, the Plesio- 

 siturus, and the Saurian reptilia: it. differs, further, from all 

 these animals in the following respect;— the body of the bone 

 is not perforated by a canal for the inferior maxillary nerve; 

 in place of which is observed a groove running the whole 



■ Conybearc. 



3F2 length 



