148 Annals of the South African Museum. 



GENUS TRAPEZIUM Megerle von Miihlfeldt. 



TRAPEZIUM? TATEI sp. nov. 

 Plate VII., figs. 13, 13a. 



Description. The shell is well elevated in figure, with the umbonal 

 region rising prominently, and well removed from the anterior 

 extremity. The cardinal margin is almost straight posteriorly to the 

 limbo, and slopes back to form a rounded obtuse angle with the 

 straight, very steeply falling posterior border. In front of the umbo 

 the margin falls rapidly, with slightly convex outline, to the sharply 

 convex anterior border. The inferior margin gives a broadly convex 

 outline, and has a sharply angular junction with the posterior 

 border. The greatest height occurs at the uinbo, the greatest con- 

 vexity at about the middle of the valve. 



On the posterior side of the valve a sharp carinal ridge passes 

 in steeply inclined direction from just behind the umbonal apex to 

 the postero-inferior angle of the valve-margin. This carina marks 

 off a very well-defined, flattened posterior area, the surface of which 

 is inclined at a sharp angle to that of the remainder of the valve. 

 The valve-surface is devoid of sculpture, but is marked by numerous 

 delicate lines of growth. 



Dimensions. (1) (2) 



Length 9'5 . 14mm. 



Height 8 . 12 



Depth of a single valve . 4 ,, 



Occurrence. Found on the left side of the Coega Valley, half a 

 mile down from the railway (452g). An imperfect left valve, 

 apparently of the same species, occurring in the same hand-specimen 

 with Solecurtus sp. and Meretrix uitenhagensis (310), was found at 

 Grass Ridge, three miles east-north-east of Uitenhage. 



Remarks. Unfortunately there is only a single perfect specimen, 

 a left valve, available for description, but this is very well preserved, 

 although the interior characters cannot be studied. 



Another shell of still more doubtful generic position, with which 

 this form is comparable in some respects, is Corbula ? rockiana 

 Tate.* The general habit is very similar, but a very careful com- 

 parison with Tate's type-specimen (number 11023 in the collection of 

 the Geological Society) seems to preclude any idea of uniting these 

 two forms. Tate's species is less elongated, more elevated in figure, 

 and considerably more inflated, particularly in the umbonal region, 



* Tate (1), p. 159, pi. viii., fig. 8. 



