80 Albany Museum Records. 



to the prepai'ietal of the S. Afi-ican forms. By Newton ("") it is 

 regarded as the interparietal. 



It wonkl thvis appear that the preparietal occurs in the 

 majority of the Anomodont genera. It is unknown in the 

 Therio(U)nts, the Therocephalians or the Pareiasanrians, and wonkl 

 thns appear to be a new element that has arisen in the Anomodont. 

 Thongh in all probability it has originated as a woi'mian bone, its 

 occurrence in a number of very dissimilar genera, and its occa- 

 sional large development seem to entitle it to a distinctive name. 



IV.— The Mandible. 



Though a good many descriptions have been given of the 

 bones of the mandible, there are still a few points that are obscure. 

 As the result of the examination of specimens in the Albany 

 Museum. I can now, however, give pretty full details of the 

 structure of the mandible in Lystrosaurus ; while specimens in 

 my own collection reveal fully the structure of all the elements in 

 the lower jaw of Oudenodun. 



In Lystrosaurus the mandible is composed of the usual five 

 elements. - dentary, angular, surangular, splenial and articular. 

 The dentai'ies of the two sides are firmly anchylosed, as in the 

 tortoise, antl form approximately the anterior halves of the jaws. 

 The splenials, if not anchylosed, are closely united to each other, 

 and form the lower part of the front of the beak ; and they add 

 considerably to the strength of the beak by forming a sort of axis 

 round which the dentaries ai*e formed. The surangular is a 

 moderate-sized element which forms the upper part of the posterior 

 half of the jaw. In front it articulates with the dentary al)ove the 

 large vacuity of the jaw, the surangular lying to the inside of the 

 dentary. Posteriorly it forms a large articulation with the articu- 

 lar, the surangular passing between the articular on the inside 

 and the angular on the outside. The large vacuity of the jaw 

 separates the anterior part of the surangular from the angulai-. 

 The angular is a fairly large element of a most irregular shape. 

 It sends a long slender process forward below the vacuity to 

 articulate with the dentary and the splenial. This anterior process 

 passes inside of the dentary and between the dentary and the 

 splenial. On passing backwards the angular forms a deep fan-like 

 expansion of which the lower part forms a well-developed process 

 which i)ass('S downwai'ds, backwards and slightly inwards. The 

 U|)pcr I ait of the fan like postei-ior part rests on the articular and 



