FROM TANGANYIKA AND KENYA 27 



Nuculana (Dacryomya) dodsoni sp. nov. 

 PL 1, figs. 2a, b, c 



Specific name. After Mr. R. G. Dodson, of the Geological Survey of Kenya. 



Diagnosis. Of medium size (length of largest specimens 15 mm.), pyriform, with 

 the height slightly exceeding half the length ; inflation moderate ; with strongly 

 opisthogyrous umbones placed just anterior to mid-length and a slightly upcurved 

 posterior rostrum, the extemity of which is truncated and situated below mid-height. 

 Postero-dorsal outline strongly concave ; antero-dorsal outline and anterior and 

 ventral margins forming an uninterrupted, parabolic curve, the ventral margin 

 convex as far as its posterior extremity. External features of shell unknown. 



Holotype and paratypes. Numerous internal moulds exposed, together with 

 moulds of a species of Nucula, on a bedding plane of hard brownish limestone. The 

 holotype (no. L. 98280) is the specimen represented in PL 1, fig. 2c. 



Locality and horizon. Hagardulun, 25 miles N.E. of Tarbaj, N.E. Kenya ; 

 Bathonian-Callovian, Bur Mayo Limestones. 



Remarks. Nuculana decorata (Douville) (1916 : 61, pi. 5, figs. 56-62), Bathonian 

 of Sinai, is very similar to this species, but differs in its broader umbonal region. 

 The widespread Bathonian species N. lacryma (J. de C. Sowerby) has a more sharply 

 pointed and upcurved rostrum and a more strongly convex ventral margin. The 

 Callovian species N. moreana (d'Orbigny) (types figured by Cottreau 1925 : 12, pi. 

 38, figs. 4, 5), which is doubtfully distinct from N. lacryma, differs in the same manner. 

 The Toarcian-Aalenian species N. rostralis (Lamarck) (type figured by Favre 1914, 

 pi. 35, figs. 242a, b) has less prominent umbones and a less strongly concave postero- 

 dorsal margin. The Oxfordian species N. acuta (de Loriol) (1899 : 164, pi. 10, figs. 

 29-32, ex Merian, MS.) has a narrower posterior extremity, a less concave postero- 

 dorsal margin, and a distinct sinus at the posterior end of the ventral margin. N. 

 matheyi (Rollier) (1912 : 62, pi. 6, fig. 5), another Oxfordian species, has a less 

 prominent umbo. 



Subgenus RYDERIA Wilton 1830 



Nuculana (Ryderia) kenyana sp. nov. 

 PL 1, figs. 6a, b, c 



Diagnosis. Of medium size (height up to 9 mm., original length possibly three 

 times that amount), very compressed, inequilateral, with an evidently long posterior 

 rostrum, the extremity of which, however, is broken away in all the specimens. 

 Umbones very obtuse, only feebly opisthogyrous, level with the almost straight, sub- 

 horizontal antero-dorsal margin. Anterior margin flattened, forming an obtuse 

 angle with antero-dorsal margin ; ventral margin almost straight except for a slight 

 sinus at beginning of posterior rostrum. Postero-dorsal outline feebly concave ; 

 escutcheon narrow, shallow, bordered by umbonal ridges which are well defined only 



