124 REPORT — 1839. 



If, as I have conceived, the pectoral fin and the massive 

 sterno-coracoid arch relate to occasional reptation on the sea- 

 shore, it may be inferred from the partial flattening of the 

 articular surfaces of the vertebrae, in a species characterized by 

 a greater size and strength of the fore paddles, that it was more 

 terrestrial or littoral in its habits than the ordinary Ichthyo- 

 sauri. 



Ichthyosaurus thyreospondylus. 



In the museum of the Bristol Institution there are five verte- 

 brae of an Ichthyosaurus, of a compressed subpentagonal form ; 

 one of these, which has a vertical diameter of two inches and 

 a half, and a transverse one of two inches and a quarter, is 

 only nine lines in antero- posterior extent. The articular sur- 

 faces for the ribs are developed into short transverse processes, 

 the upper one projecting immediately beneath the neurapophy- 

 sial pit, and the lower one an inch lower down, and near the 

 anterior margin ; the anterior and posterior articular surfaces 

 are concave, but have a convex rising, in the form of the heraldic 

 fess, the base being equal to the breadth of the surface support- 

 ing the medulla spinalis, and the apex reaching to the centre of 

 the articular surface. This character I have not observed in 

 the vertebrae of any other species of Ichthyosaurus. 



Ichthyosaurus trigonus. 



I have been favoured by Miss Benett, of Norton House, 

 Warminster, with some rare specimens from her valuable col- 

 lection of fossil remains, among which is the body of a vertebra 

 of an Ichthyosaurus remarkable for the straightness of the 

 sides below the transverse process, from which point they con- 

 verge at an angle of 70°; the upper part of the body of the 

 vertebra, which supports the spinal and neurapophysial sur- 

 faces, is the broadest, and is bounded by a horizontal straight 

 line, the whole presenting a triangular contour. The well- 

 marked distinctions which this vertebra presents as compared 

 with any that I have seen which belong to the preceding 

 species, embolden me to regard it as indicative of a distinct 

 species, for which a provisional name is proposed expressive of 

 the form of the vertebra. 



The anterior and posterior articular surfaces present the 

 usual concavity : the non-articular surfaces at the sides of the 

 vertebra are smooth. 



Inch. Lines. 



The antero-posterior diameter of this vertebra is 1 



The transverse diameter 2 6 



The vertical diameter 2 10 



Locality. — Westbrooke, in Bromham, Wilts ; Kimmeridge 

 Clay. 



