338 



Prof. H. G. Seeley. 



[May 12, 



The suture between the pre-maxillary and maxillary bones is over- 

 lapped by a triangular sub-nasal bone, and the pre-maxillaries are 

 apparently small, as in Amphibians. The maxillary bone has a row of 

 large supra-dental foramina. The malar bone is excluded from the 

 alveolar border of the jaw. Behind the orbits the bones which form 

 the cheeks are arranged as in Labyrinthodonts, and completely cover 

 the quadrate bone as in Labyrinthodontia and Ichthyopterygia. They 

 include the post-orbital, post-frontal, squamosal, supra-temporal, and 

 quadrato-jugal, which is of large size. The roof bones of the head 

 are the nasal bones, pre-frontals, (?) the supra-orbital, frontals, 

 parietals, (?) supra- occipital, and epiotic. 



The occipital condyle, though imperfectly preserved, was single and 

 formed by one bone, which is named basi-occipital, and regarded as 

 being an inter-central ossification of the vertebral column, which has 

 been received between the exoccipital bones of the Labyrinthodont 

 skull, but which has not penetrated so deeply between them as in 

 typical Anomodonts. The nearest approach to this condition of the 

 occipital condyle is seen in Ichthyosaurus. The composite character 

 of the occipital condyle in Anomodontia, Chelonia, Rhynchocephalia, 

 Crocodilia, Sauropterygia, Aves, &c.,is accordingly regarded as due to 

 the preservation of the original Labyrinthodont exoccipital elements 

 in union with the new basi-occipital element. And the mammalian 

 return to articulation of the skull by exoccipital condyles is attributed 

 to expansion of the brain which caused the basi-occipital bone to enter 

 into the floor of the brain case. 



The structure of the palate is described, and shown to resemble that 

 of Anomodonts, certain Labyrinthodonts, and the embryonic forms 

 of existing Amphibia in which the para-sphenoid has not been 

 ossified. 



The lower jaw encloses a long chamber which extends beneath the 

 teeth as in Labyrinthodonts. 



The dentition is described, and is chiefly remarkable for the uniform 

 character of the teeth, for their distinctive shape, mode of union with 

 the jaw, and replacement by successional teeth, which are developed 

 as in Ichthyosaurs. 



The skull is compared with the skulls of the types of P. serridens 

 (Owen) and P. bombidens (Owen) ; and the author concludes that 

 there is no satisfactory dental character to distinguish the described 

 species from each other, and rests their differentiation upon the 

 forms, proportions, and structure of the head. 



Comparison is then made of the cranial characters in which 

 Parieasaurus resembles other animals, so as to show how far the 

 Labyrinthodont characters are common to Fossil Reptilia, and 

 how far the supposed Dinosaurian characters may be otherwise 

 regarded. 



