194 LABYEINTHODONTIA. 



internally, and is thus more crescent-like. It exhibits 

 facets for the capitula of the ribs on the posterior border 

 of the upper extremity of the outer surface. Ehachitomous 

 vertebrae from the Karoo system of the Cape are preserved 

 in the Museum at Munich (as the writer is informed by 

 Dr. E. Eraas), which may belong either to the present 

 form or to Rhytidosteus. 



Presented by Sir R. Owen, K.C.B., 1884. 



Genus RHYTIDOSTEUS, Owen 1 . 



Skull depressed an d relatively short ; orbits situated in the pos- 

 terior half, and separated from one another by the whole width of 

 the cranium ; nares placed far behind the muzzle, directed laterally, 

 and likewise separated by the whole width of the cranium ; occipital 

 region unknown ; palate extensively ossified, without vacuities near 

 the medial line (so far as shown). Mandible without alveolar 

 parapet, but with a postarticular process. A row of comparatively 

 small premaxillary and maxillary teeth, and on either side of the 

 hinder maxillary teeth an irregular series of denticules, while 

 smaller denticules spread out over the palate; one large tusk in 

 advance of, and another behind, the posterior nares ; a series of 

 denticules on either side of the marginal row of mandibular teeth. 

 Teeth with complex foldings and large pulp-cavity. Sculpture 

 coarsely radiate, with an indistinct lyra between orbits and nares. 



This genus is referred to the present group on account of the 

 presence of denticules on the jaws, by which it appears to be allied to 

 Eryops. The full ossification of the palate differs, however, so re- 

 markably from that of Archegosaurus, that the genus should probably 

 be referred to another family. Whether, however, it should form 

 the type of a distinct family (in which Eryojps should probably be 

 included) or should be classed with the Nyraniidce, cannot be deter- 

 mined until the relations of the bones of the palate are fully known. 

 The position of the orbits in the present genus is quite peculiar. 



Rhytidosteus capensis, Owen 2 . 

 The type and only described species. Length of skull probably 

 about 0,250 (9*8 inches) ; muzzle very broad and blunt. 

 Hob. South Africa. 



R. 455. The flattened skull, wanting the posterior portion of the 



{Fig.) cranium, and with the mandible imperfect; from the 



Karoo system of Beersheba, Orange Eree State. The type 



specimen ; figured by Owen in the ' Quart. Journ. Geol. 



1 Quart. Journ. Geol. Soc. vol. zL p. 333 (1884). 



2 Loc. cit. 



