FROM TANGANYIKA AND KENYA 171 



almost smooth. Muller's fig. 12 indicates that the spiral threads ornamenting the 

 whorls of N. mnelleri bear more conspicuous granules than have been observed in 

 Tendaguru specimens, but the granules may have been exaggerated by the artist. 

 A more noticeable difference lies in the shape of the labral fold, which Muller's fig. 13 

 shows to be relatively slender where it joins the outer lip and to split up distally into 

 two branches of appreciable length. In Tendaguru specimens the corresponding 

 fold is broad at its base and its outline is either triangular or square, at times with 

 slightly projecting angles. This difference, considered in conjunction with the much 

 higher stratigraphical horizon, seems to justify the recognition of the Tendaguru 

 Nerinella as a species distinct from N. muelleri. Of European species, N. damisensis 

 (d'Orbigny) (1852 : 118, pi. 267, figs. 4-6) has a labral fold rather similar in cross- 

 section to that of the Tendaguru species, but its whorls are more strongly concave 

 and more coarsely ornamented. 



The specimens from the Seir Limestones of N.E. Kenya consist of partly weathered- 

 out shells on the surface of a bed of hard limestone. Their surface features are not 

 preserved, but erosion has exposed the internal structure of some of the shells, which 

 include specimens with folds agreeing well with those of N. cutleri, particularly as 

 regards the shape of the one on the outer lip. Other genera are also represented. 



Nerinella mandawaensis sp. now 



PL 30, figs. 1, 2a, b, 3 



Diagnosis. Shell very slender, the largest specimens having a maximum dia- 

 meter of 6-5 mm. and an estimated length, when complete, of about 10 cm. Whorls 

 moderately concave, with the sutural region forming a swollen band ; height of 

 whorls slightly exceeding their diameter. Ornament consisting of granose spiral 

 threads ; some specimens with four primary ones throughout, with weak interstitials, 

 other specimens with up to eight threads on later whorls, where they differ very little 

 in strength but are distributed irregularly. One not very prominent internal fold 

 on the lower part of the columella ; one narrow, thorn-like parietal fold occupying 

 the angle between the columella and the upper wall of the whorl ; and one prominent 

 but only moderately broad fold, widening slightly at its distal end in some specimens, 

 just below the middle of the outer wall. 



Holotype and paratypes. Nos. GG.10333, GG.10334-38 respectively, the para- 

 types in pieces of sandstone some containing several specimens. 



Locality and horizon. Along Mandawa-Namakongoro stream, about i mile 

 W. of Mandawa, Tanganyika ; Middle-Upper Kimmeridgian. 



Remarks. The specimens are of the same age as Nerinella cutleri, from Tenda- 

 guru, but their recognition as a distinct species is justified by their more strongly 

 concave whorls and by the differences in their internal folds. The labral fold, in 

 particular, is narrower but more prominent than that of the Tendaguru form. 



