146 BRITISH FOSSIL REPTILES. 



clilian, witli characters indicative of a Steneosaur; it is embedded in its matrix, and' 

 includes the upper part of a cranium with much of the bony roof broken away ; 

 this mutilation, however, exposes the cranial cavity, a cast of which gives a toler- 

 ably good representation of the brain of the extinct reptile. The cerebral lobes, 

 thus shown, have the smooth convexity of those of the Crocodile, and the similarly 

 smooth optic lobes, but little less in size, are partially represented. The length of 

 so much of the brain is 2 inches, the breadth of the cerebrum is 1-| inches ; the 

 breadth of the skull is 6|- inches. The temporal fossae form wide ellipses 2 inches 

 9 lines in long diameter. From the back of the cranium to the beginning of the 

 narrowing jaws is 8 inches; the length of the skeleton maybe estimated as about 

 18 feet. 



John Hunter had acquired for his series of evidences of extinct species — so 

 remarkable at that period — a century ago — a portion of the mandible of a Steneosaur, 

 including six inches extent of the hind part of the symphysis : the transverse 

 diameter of the mandible at the junction of the rami is 4 inches, 3 lines ;. 

 the hind surface of this union shows a deep transversely elliptical depression. 

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

 outer sides of the rami here are nearly flat and at right angles with the horizontal 

 surfaces, the angles being rounded oS". The inferior flattened surface is impressed 

 with small irregular longitudinal grooves, but not with pits or foramina. So 

 much of the alveolar border is preserved in each ramus as measures 6-|- inches ; 

 the inner border rises higher than the outer one, and this tract includes eight 

 teeth of Steneosaurian character : the diameter of the circular base of the crown is 

 from 4 to 5 lines. 



So much of the matrix as remains attached to this specimen resembles Oxford 

 oolite. It is not without interest to see that the geologically younger Protosuchian 

 shows narial and some slighter characters, by which it comes nearer to the modern 

 gavialic modification of the order ; but the species of the genus next to be 

 described, which have left their remains in still later mesozoic deposits, make a 

 still nearer approach to the existing forms of CrocodiHan Reptiles. 



Gew(s— PLESIOSUCHUS, Owen,'' 

 Species — FJestosuchus ManselUi," GrocodlUa (PI. 20, figs. 1 — 4). 



This genus and species exemplifies an interesting approach in an upper division 



1 irXeo-ios, near; avyos, Crocodile (name of Egyptian species). 



^ Steneosmiriis Manselii, Hulk, ' Quarterly Journal of the Geological Society,' vol. xxvi, p. 170, 

 pi. is. 



