MESOSATJKIA OF SOTJTH AFEICA. 591 



developed abdominal ribs, formed of flattened plates, give its most 



distinctive feature, and it is probable that 



the species is different from the slender deli- Pig, 1. 



cate type-species, with elongated teeth. It 



makes known the remainder of the skeleton, 



with the exception of the pelvis and sacrum, 



the femur, tibia, and fibula, and the extremity 



of the tail. 



There are some points in which it appears 

 to me that the Mesosaurian shoulder-girdle 

 fi.gured by Gcrvais may be given a different 

 contour, but the evidence in favour of this ch = chevron bone, 

 change in interpretation will be better ap- 

 preciated after the discussion of a new specimen which is preserved 

 in the South African Museum, Cape Town. 



§ 3. The Mesosauetjs tenfidens (Geevais) feom Albania. 



The Cape Town fossil was collected by David Arnott in the dis- 

 trict of Albania in Griqualand West. It is in white fissile marl, 

 and, as in all other similar specimens, the bones have disappeared 

 and left an internal mould of the skeleton. The slab unfortunately 

 only shows the ventral aspect of the anterior part of the skeleton. 

 It appeared at first as though the skull had a short triangular form, 

 but by careful development from the matrix it is proved to have had 

 the same elongated form of head which characterizes the Paris type ; 

 and, indeed, it extended beyond the limit of the slab. 



As preserved, the lower jaw is 5 centimetres long. The rami 

 are narrow in the articular region, beyond which they are prolonged 

 backward in a heel. The transverse width over the articular region 

 is about 1-5 centimetre. The rami widen as they extend forward, 

 though this condition may be, in part at least, the effect of com- 

 pression, since a median channel extends along the symphysis, of 

 which not more than 1 centimetre is preserved. The transverse 

 width at the anterior fracture exceeds | centimetre. The external 

 surface of the bone is somewhat uneven and marked with longitudinal 

 striations. Behind the acute anterior convergence of the rami the 

 palate is exposed. It is completely closed, without indication of 

 any vacuity. Two elevated ridges nearly parallel to each other and 

 close together extend along its length and converge backward. There 

 is a possibility that these ridges carried single rows of teeth like the 

 teeth on the ridges on the palate of Pareiasaiirus, as the impression 

 from the cast shows at regular intervals a few white dots along 

 each ridge. The ridges become more elevated at the back of the 

 palate and diverge outward and backward in a Y-shape to the 

 articular region, which is strongly suggestive of the pterygoid bones 

 abutting against the basi-sphenoid. It is possible that the palate- 

 nares may be in the depression behind the posterior divergence of 

 the pterygoid bones. On the hinder part of the pterygoid region 

 are short slender rods which appear to be part of the hyoid. 



