152 Annals of the South African Museum. 



Dimensions.- (1) (2) (3) (4) 



Length 14 . 16 . 17 20mm. 



Height, measured at the 



middle of the valve 11 . 12 . 13 16 



Greatest depth of a 



single valve 3 . 3'5 . 3'5 4 ,, 



Occurrence. Found in the kloof east-north-east of Eed House, on 

 the left side of the Zwartkop's Eiver (324), and at Grass Eidge, three 

 miles east-north-east of Uitenhage (310) ; also in the railway cutting 

 between milestones 24|-24f on the line from Uitenhage to Graaff- 

 Eeinet, about three miles from Uitenhage (316). A specimen sent 

 from the South African Museum is from the Sunday's Eiver, 

 occurring with HolcostepJianus cf. atherstoni (Sharpe). Mr. Eogers 

 obtained specimens of this form, in 1905, from the left side of 

 Coega Valley, half a mile down from the railway (453g, 454g) ; 

 from a bare slope, W. 30 S. from the middle of Barkly Bridge, 

 on the farm Olifant's Kop, Sunday's Eiver (24h, 26h, 28h-30h) ; 

 and from the highest beds in the kloof behind Colchester, left bank 

 of Sunday's Eiver (493g, 498g). 



Remarks. Although this elegant shell shows some variation in 

 outline and in the degree of inflation, yet the individuals here brought 

 together agree on the whole very closely and are well characterised. 

 The chief features of the shell are the generally rounded and soft 

 outline, the inconspicuous, rounded umbonal region, and the very 

 compressed form of the valves. 



In outline, the shell resembles some specimens of Venus 

 orbignyana Forbes," from the Lower Greensand of the Isle of 

 Wight, which differs, however, by the considerably stronger inflation 

 and the more marked anterior excavation under the umbones. 

 Meretrix uitenhagensis has a less steeply sloping upper margin 

 posteriorly to the umbones, and the umbones are less prominent. 

 The minute concentric linear striee are developed also in Venus 

 orbignyana, though more faintly marked than in the African shell. 



Meretrix parva (Sow.),t also from the Lower Greensand of 

 England, is more circular in outline, more nearly equilateral, and 

 considerably more inflated in form. 



Meretrix brongniarti (Leymerie)J is a larger and more massive 

 shell, and even if compared at the same dimensions is seen to be more 

 elongated and posteriorly attenuated in outline, and more equilateral. 



* Forbes (1), p. 240, pi. ii., fig. 5. 



t J. de C. Sowerby (1), vol. vi., Tab. 518, figs. 4-6 (1826). 



{ Leymerie (2), p. 5, pi. v., fig. 7; pi. vii., fig. 1. 



