A TELE08AUK PROM THE WHITBY LIAS. 633 



of the tympanic cavity, but no satisfactory suture can be distin- 

 guished between it and the exoccipital bone. It is in the position of 

 the prootic bone of the CrocodUe, but is enormously developed so as 

 to present the most distinctive feature of the cranial region of a Teleo- 

 saur. This bone, which is imperfectly preserved at its outer and 

 posterior border, has a nearly vertical anterior suture less than 4 

 centimetres long, like that in living Crocodiles, a straight inferior 

 suture, and a curved superior outline, determined by the overlap of 

 the parietal bone. The bone is wider in front than behind : its 

 greatest depth is 4| centimetres ; its greatest length, as preserved, 

 71 centimetres ; its surface is smooth and concave. Almost im- 

 mediately below the anterior suture of this bone, at a distance of 

 about a centimetre, and looking on to the under part of the skull, is 

 a large transversely ovate perforation with rounded borders, 2 centi- 

 metres in length, into which it does not enter. This is, I presume, 

 the outlet for the fifth nerve (fig. 3, V). It is placed just behind the 

 pituitary body. If this perforation is rightly determined, and the 

 nomenclature adopted by Professor Huxley is followed, the bone 

 which lies in front of this perforation is the alisphenoid ; and if the 

 orbito -sphenoid has any separate existence, the condition of the spe- 

 cimen is such that it cannot be recognized. But if we were rather 

 to name the bone alisphenoid which unites with the basisphenoid, 

 following the nomenclature of Prof. Owen, then the orbito-sphenoid 

 would form the anterior wall of the brain-case. The bone posterior 

 to the nerve-outlets is certainly the quadrate, as in living Crocodiles. 

 In perfect Teleosaur skulls it meets the squamosal above and the ex- 

 occipital behind ; and it forms the anterior and inferior wall of the 

 tympanic cavity. The anterior wall of the brain-case or alisphenoid 

 (als) is imperfectly preserved anteriorly. It is a large oblong bone, 

 concave and irregular on the underside, where the pterygoid lapped 

 along its length, slightly concave in length above, and slightly con- 

 vex from above downward. It appears to be about 6 centimetres 

 deep, and the greater part of it lies above the longitudinal angular 

 ridge running along it already alluded to. Owing to the form of 

 the parietal it is much deeper behind than in front. The base of 

 the skull is too much worn for useful description. 



So far as I can judge by comparison with the type specimens in 

 the British Museum, this species difi'ers materially in the outer shape 

 of the brain-case from the Teleosaurus GTiapmani, The Teleosaurus 

 brevior is too imperfectly preserved in this region for satisfactory 

 comparison. I am not acquainted with any species from the 

 Secondary rocks which closely resembles this species in the form of 

 the prootic bone, or of the tympanic region, or the general shape of 

 the brain-case. As its characters are likely to be of some interest, 

 it may be useful to name the species for the present Teleosaurus 

 eucepJialus. 



