4 ME. G-. A. BOULENGEE ON A NOTHOSAUEIAN EEPTILE 



Among the points on which there can be no doubt may be mentioned the very anterior 

 opening of the choanse, separated by a narrow septum formed by the vomers ; the 

 presence of large oval suborbital vacuities, such as are known to exist in Neustico- 

 saurus, and as are shown on Curioni's figure ; and the backward extension and union 

 on the median line of the pterygoids, as far back as the basioccipital, which they cover 

 over, as well as the basisphenoid, in this respect agreeing with most Nothosaurians. 

 These pterygoids are produced and narrowed anteriorly, where they join the vomers, 

 whilst posteriorly they form two raised ridges on each side, between which the quadrate 

 is wedged in. Before the skull had been thoroughly cleared from the matrix, the 

 outer of these ridges conveyed to my mind the remains of ossified hyoid cornua (cerato- 

 branchials). But, in the course of development, these ridges were found to bear a 

 series of minute subconical teeth. This discovery is a very startling one, for, unless 

 the Placodonts belong to the Plesiosauria, no member of this order was yet known 

 to have possessed teeth on any of the bones of the palate. It is true that the 

 following remark is made by Prof. Seeley (25, p. 591) respecting Mesosaurus tenui- 

 dens : — " Two elevated ridges, nearly parallel to each other and close together, extend 

 along its [the palate's] length, and converge backward. There is a possibility that 

 these ridges carried single rows of teeth like the teeth on the ridges on the palate of 

 Pareiasaurus, as the impression from the cast shows at regular intervals a few white 

 dots along each ridge." 



The bone between the suborbital and subtemporal fossae I take to be the ecto- 

 pterygoid, known to be largely developed in Simosaurus, but absent from the restora- 

 tions of Nothosaurus. Hence, the palatines would be small, and relegated to between 

 the choanae and the suborbital fossae. 



The mandible has a short symphysis, with median suture, and projects posteriorly 

 considerably beyond its articulation with the cranium ; on this process the angular, 

 supra-angular, and articular bones are perfectly distinguishable. 



The neck consists of 21 vertebra?. Its length is once and a half that of the skull, 

 and nearly equals that of the body. The vertebrae are short, the centra being a little 

 broader than long ; they bear short ribs, which are fork-headed, as is clearly shown on 

 the counter-plate which bears the right rib of the second vertebra, and further by a 

 detached rib lying on the right side of the eighteenth vertebra (fig. 2). The dislocated 

 seventeenth vertebra shows the posterior articular surface moderately cupped. The 

 atlas shows the proatlanto-atlantic hypapophysis separating the neuroids, and followed 

 by the centrum, behind which there is no hypapophysis. 



Little is to be seen of the dorsal vertebral column and ribs, obscured as they are by 

 the overlying pectoral arch and plastron ; the number of vertebras may be computed at 

 about 20. 



The tail is long and slender, tapering to a fine point ; its length is nearly three times 

 that of the skull ; it comprises 42 or 43 vertebrae. 



