Geological Society. 483 



March 9, 1881.— Robert Etheridge, Esq., F.R.S., 

 President, in the Chair. 



The following communications were read : — 



1. " Description of Parts of the Skeleton of an Anomodont Reptile 

 (Plutypodosaurus robustus, Ow.). — Part II. The Pelvis." By Prof. 

 Owen, C.B., F.R.S., F.G.S., &c. 



In this paper the author described the remains of the pelvis of 

 Plati/podosaarus rohustm which have now been relieved from the 

 matrix, including the sacrum, the right " os innominatum," and a 

 great part of the left ilium. There are five sacral vertebrae, which 

 the author believes to be the total number in Platypodosaurus. 

 The neural canal of the last lumbar vertebra is 8 lines in diameter, 

 and of the first sacral 9 lines, diminishing to 6 lines in the fifth, 

 and indicating an expansion of the myelou in the sacral region, which 

 is in accordance with the great development of the hind limbs. The 

 sacral vertebrae increase in width to the third ; the fourth has the 

 widest centrum. This coalescence of the vertebrae justifies the con- 

 sideration of the mass, as in Mammalia, as one bone or " sacrum," 

 which may be regarded as approaching in shape that of the Mega- 

 therioid Mammals, although including fewer vertebrae. Its length 

 is Tg inches ; its greatest breadth, at the third vertebra, 5| inches. 

 The ilium forms the anterior and dorsal walls of the acetabulum, the 

 posterior and postero-ventral walls of which are formed by the ischium 

 and pubis. The diameter of its outlet is 3 inches, the depth of the 

 cavity Ij inch ; at its bottom is a fossa 1^ inch broad. The fora- 

 men is subcireular, 1 inch in diameter. The ventral waU of the 

 pelvic outlet is chiefly formed by the pubis ; it is a plate of bone 

 6 inches broad, concave externally, convex towards the pelvic 

 cavity. The subacetabular border is 7-8 lines thick ; it shows no 

 indication of a pectineal process, or of a prominence for the support 

 of a marsupial bone. The author remarks that of aU examples of 

 pelvic structure in extinct Reptilia this departs furthest from any 

 modification known in existing types, and makes the nearest ap- 

 proach to the Mammalian pelvis. This is shown especially by the 

 number of sacral vertebrae and their breadth, by the breadth of the 

 iliac bones, and by the extent of confluence of the expanded ischia 

 and pubes. 



2. " On the Order Theriodontia, with a Description of a new 

 Genus and Species (^lurosaunts felinus, Ow.). By Prof. Owen, 

 C.B., F.R,S., F.G.S. 



The new form of Theriodont reptile described by the author in 

 this paper under the name of JERurosaunts felinus is represented by 

 a skuU with the lower jaw, obtained by Mr. Thomas Bain from the 

 Trias of Gough, in the Karoo district of South Africa, The post- 

 orbital part is broken away. The animal is mononarial ; the alve- 

 olar border of the upper jaw is slightly sinuous, concave above the 



