ON BRITISH FOSSIL REPTILES. 83 



angle is equal in length to the transverse diameter of the articular surface, ap- 

 proaching thus to Plesiosaurian proportions, whilst it is longer in the Gavial and 

 in Teleosaurus. The articular surface is convex in the middle and concave on 

 each side, as in the Teleosaurus, and not regularly concave, as in Gavial : the 

 articular piece is continued more forwards, and is stronger upon the internal 

 side of the i-amus. The depth of the ramus at the coronoid ridge is greater, and 

 the coronoid ridge itself is higher : there is no interspace between the an- 

 gular and surangular elements*. From the angle to the beginning of the 

 symphysis of the jaw is 1 foot 9 inches, the depth of the jaw at the coronoid 

 process is 4 inches. The nostrils are bounded by short intermaxillaries, 

 each of which contains three teeth. Both intermaxillary and maxillary teeth 

 are larger in proportion than in Teleosaurus. The maxillary teeth are ar- 

 ranged closer together as they are placed further back. In a fragment of 

 jaw containing three teeth, these are placed obliquely in sockets, from two 

 to three lines apart. The fang is covered by a smooth white cement ; the 

 crown with a black enamel, traversed by fine longitudinal, close-set, inter- 

 rupted ridges, one on each side of the tooth, is stronger than the rest, and 

 meeting, in the unworn teeth, upon an obtuse summit. 



In a fragment of a lower jaw of apparently the same species of Steneosaurus, 

 in the Hunterian Collection, which includes 6 inches of the posterior com- 

 mencement of the symphysis, the transverse diameter, at the junction of 

 the rami, is 4 inches 3 lines : the middle of the posterior surface of the 

 junction is excavated by a deep transversely elliptical depression. Both the 

 upper and lower surfaces of this portion of jaw are flat, and the sides are 

 nearly flat, and on right angles with the horizontal surfaces ; the intervening 

 angles being rounded off". The inner border of the alveolar tract is higher 

 than the outer. The inferior flattened surface is impressed with some small, 

 irregular, longitudinal vascular grooves, but not with pits or foramina. Eight 

 teeth are contained in an extent of the alveolar tract measuring 5^ inches. 

 The diameter of the circular base of the crown of the tooth is from four to 

 five lines. The matrix appears to be oolite ; the cavities in the crowns of 

 the teeth are filled with white spar. 



Perhaps the most interesting fact which has resulted from an examination 

 of the British fossils of the present genus is the size and form of the brain, 

 as exhibited by an internal cast of the cranial cavity. 



In the museum of Professor Sedgwick there is a slab, in which the head 

 of a Steneosaurus is imbedded, the upper part being exposed, from which a 

 considerable part of the bony substance has been broken away, and, amongst 

 the rest, the whole upper wall of the cranial cavity, exposing a tolerably per- 

 fect cast of its interior, which represents the brain of the extinct reptile. 

 This cast resembles the smooth convex cerebral lobes of the Crocodile, and a 

 portion of the large optic lobes which lie posterior to them. The cerebrum 

 is 1^ inch in breadth, and the whole of the brain represented by this cast is 

 2 inches in length. The breadth of this head is 6-^ inches. The temporal 

 openings form wide ellipses, 2 inches 9 lines in the long diameter : from the 

 back of the cranium to the commencement of the narrow elongated jaws is 8 

 inches ; from these proportions the length of the individual may be calculated 

 at about 18 feet. 



* In the thin, long and slender jaws ascribed to the Poikilopleuron by M. Deslongchamps, 

 the coronoid is not raised, and there is an oblong vacuity between the angular and suran- 

 gular. 



g2 



