SOME SOUTH AFRICAN MARINE SHELLS. 3 



or strias. The concentric lines of growth are crowded 

 and wavy, and in the grooves between the riblets there is 

 in places a somewhat punctate appearance. Four or five 

 concentric waves or ridges at fairly equal distances fi-om 

 the foramen may indicate periods of arrested growth. The 

 subapical hole is very anterior, oblique in front of the apex, 

 and the front slope beneath it is considerably concave- 

 Considering the lightness of the external costulation, the 

 margin is distinctly denticulate, the grooves between the 

 denticles extending within a little distance from the edge. 

 The denticles are about eighty in number, and those upon 

 the anterior end are often sub-bipartite. G. tenuistriata 

 (Soioerhy) is rather like the present species as regards foi-m, 

 but the sculpture is not the same. In the largest specimen 

 examined the colour rays are very faint, probably through 

 fading. A smaller and fresher specimen exhibits seven rays 

 — three on each side and one in front ; the two behind slope 

 posteriorly, four are inclined towards the front, the seventh 

 ray extending from near the foramen to the margin down the 

 middle of the shell. 



Tivela compressa Snverhy. PI. I, figs. 6-8. 



Hab. — Port Shepstone, Tongaat, Scottburgh (Burnup) ; 

 Isipingo (Miss Lois Trotter) ; Isezela (Miss Chapman). 



T. compressa was originally described from the Cape of 

 Good Hope, and it also occurs at Muizenberg, in False Bay, 

 and at Port Alfred. The specimens from Port Shepstone, etc., 

 differ from the typical form in having the ventral margin less 

 roundly curved, so that the valves have a more triangular 

 appearance, and the height of the shell is less in proportion to 

 the length. The pallial sinus is more acuminate and generally 

 extends beyond the middle of the valves, whereas in the normal 

 form it hardly reaches half-way across. The reddish-brown 

 posterior dorsal area appears to be a constant feature in this 

 species. It sometimes attains a length of 60 mm. 



