168 Structure, $c., of the Fossil Reptilia. [June 15, 



If the significance of these Amphibian characters is further found, 

 as I urge, in a sequence of affinity between the Sauropterygia, 

 Nothosauria, and Anomodontia, we should be justified in anticipating 

 that there might be a community of plan in the shoulder girdle of 

 those groups which would enable homologous elements to be recog- 

 nised. Until such comparisons fail, they cannot be disregarded. 



The view which I have discussed in justification of that offered 

 to the Royal Society in 1892 may be summarised in the statement 

 that the Anomodont is a type in which the precoracoid is ossified ; 

 that in the N"othosaur the precoracoid has ceased to be ossified, but is 

 represented by cartilage; while in the Plesiosaur the precoracoid 

 cartilage appears to be lost. But with this change there is no 

 change of plan in the clavicular arch, other than results from the 

 different habits of the several orders of animals and the forms of 

 the girdle bones with which the arch is associated. 



XIII. " Researches on the Structure, Organisation, and Classifi- 

 cation of the Fossil Reptilia. Part VIII. On further Evi- 

 dences of Deuterosaurus and Rhopalodon from the Permian 

 Rocks of Russia." By H. G. SEELEY, F.R.S. Received 

 June 10, 1893. 



(Abstract.) 



The author endeavours to separate the Labyrinthodont remains, 

 distinguished by having teeth anchylosed to the jaw, from such as 

 belong to animals having a Theriodont type of dentition. The 

 genera founded upon cranial fragments which show the Theriodont 

 type are Deuterosaurus ', Rhopalodon, and Dinosaurus. The skull in 

 Deuterosaurus is described from new materials, which make known 

 the structure of the palate and other cranial structures. The palate 

 is of Plesiosaurian type. The back of the skull is a vertical plate, and 

 the brain cavity rises in a long vertical tubular mass to the parietal 

 foramen. The quadrate bones descend below the foramen magnum 

 in a way that is best compared with Plesiosaurs. 



The articular end of the lower jaw is identified among bones 

 figured by von Meyer. 



The skull of Rhopalodon is nearly complete, and has a general 

 resemblance to the skull of the South African Dicynodont Ptychogna- 

 thus. The orbit is defended with a sclerotic circle of bones. Whereas 

 in Deuterosaurus there is only one molar tooth, in Rhopalodon theru 

 are apparently eight molar teeth, which have the posterior edge finely 

 serrated. 



The vertebrae are known from isolated and connected specimens 

 which indicate a larger number than usual of rib- bearing presacral 



