The Invertebrate Fauna of the Uitenhage Series. 167 



There is much closer resemblance, again, to Turbo bitropistus 

 Ascher, from the Grodischter Schichten (of Hauterivian age) in 

 Silesia.* This, however, has a relatively narrower band between the 

 two sharp marginal keels, and moreover, the surface of the shell is 

 ornamented with numerous and delicate spiral lines. 



TURBO ROGEBSI sp. nov. 

 Plate VIII., figs. 8, 8, 8b. 



Description. The shell consists of six whorls, possibly more. 

 The whorls are flattened above, and the upper surface slopes very 

 gently away from the spiral suture, terminating abruptly at a 

 prominent marginal keel which marks the upper limit of the outer 

 truncated face of the whorl. This truncated portion is straight in 

 profile in the earlier whorls, but becomes gently but distinctly 

 convex in the fourth or fifth whorls ; it is bounded below by a 

 prominent marginal spiral keel similar to the one above. Already in 

 the third whorl, a central spiral keel makes its appearance, and this 

 soon grows in strength, so that in the fourth whorl it is almost, if 

 not quite, as prominent as the two pre-existing marginal keels, and 

 subsequently it remains quite as conspicuous as these. At the com- 

 pletion of the fourth whorl, or perhaps a little before this, two 

 additional well-marked, thread-like, raised linear ornaments become 

 intercalated, one above and one below the central marginal keel. 

 The lower part of the body-whorl shows a rounded, convex surface 

 ornamented by about five delicate spiral keels, of which the upper- 

 most is the strongest and is separated by a narrow sulcus from the 

 lowest marginal keel. 



The spiral angle is about 75. The overlap of the whorls is such 

 that the suture coincides with the lowest keel of the marginal area. 

 In the earlier whorls the outwardly truncated form of the whorls 

 gives a step-like profile with vertical outer face ; in the later growth- 

 stages (about the fifth whorl) the upper surface of the whorls becomes 

 a little more convex and less abruptly demarcated from the marginal 

 face, while the latter becomes more convex and merges gradually 

 into the lower part of the whorl, so that the marginal truncation 

 becomes successively obscure and lost and the whorl attains an 

 aspect of even convexity. The mouth is then almost circular in 

 outline, with thin outer lip not showing angularity of form. In the 

 fifth whorl an indistinct and weakly developed sulcation appears on 

 the upper surface of the whorl, immediately above the upper marginal 

 keel and running parallel to it. 



* Ascher (1), p. 139 [5], pi. xii. [i.], figs, la-lc. 



