The Invertebrate Fauna of the Uitenhage Series. 151 



I have been unable to ascertain the nature of the hinge, and must 

 regard the generic determination of this form as provisional. A 

 shell having very similar outward form is Cyprina swindonensis, 

 described by the late Prof. Blake * from the Portlandian Swindon 

 Sands of England. 



GENUS MEEETEIX Lamarck (sensu lato). 



MEEETBIX UITENHAGENSIS sp. nov. 

 Plate VII., figs. 14, Ua; VIIL, figs. 1, la. 



Description. The shell is of somewhat variable ovate outline, 

 with the umbones situated at about one-third (or slightly less) of the 

 shell's total length from the anterior extremity. The shell-substance 

 is relatively thin and the aspect of the valves considerably com- 

 pressed and flattened, particularly in the lower half of the individual. 

 The cardinal margin slopes down only very gently when traced back 

 from the umbo, giving a slightly convex outline, and passes by a 

 curve into the posterior border which is evenly convex in outline, 

 or most sharply curved towards the lower part. This border 

 usually has considerably greater extent than the frontal border, 

 which is more sharply curved and limited in height by the some- 

 what rapid convergence of the upper and lower borders in front 

 of the umbo. The inferior border gives an evenly convex out- 

 line. The umbones are little-prominent and gently incurved; 

 they share in the relatively compressed character of the shell. 

 The greatest height of the valve occurs a little posteriorly to 

 the umbo. 



The surface is covered with very minute and delicate, concentric, 

 raised linear ornaments, separated by narrow, thread-like striae ; in 

 the lower half of the valve there are about eight of these raised 

 lines within the space of a millimetre. The lines are not all of 

 equal strength, nor are the interspaces equal in breadth, yet 

 they have a much greater aspect of regularity than that shown 

 by mere striae and ridges of growth. Behind the umbones, the 

 flank of each valve passes over into the well-sunk ligament space 

 without carination, but forming a rounded, blunt, pillow-like mar- 

 gin which, when observed in profile, conceals the ligament. The 

 ligament (preserved in some specimens) in an individual measur- 

 ing 14 mm. in length, extends back from the umbones for a distance 

 of 5 mm. 



* Blake (1), p. 232, pi. x., fig. 2. 



