26 JURASSIC BIVALVIA AND GASTROPODA 



Locality and horizon. 2 miles S. of Melka Dakacha, N.E. Kenya ; Upper 

 Kimmeridgian, Dakacha Limestones. 



Remarks. This small, evenly ovate specimen, which is just under 10 mm. long, 

 agrees so well in size and shape with de Loriol's figures of N. bellozanensis that there 

 seems no reason to qualify its identification. Of other comparable species, Nucula 

 saxatilis Contejean (i860 : 284, pi. 21, fig. 13), from the Kimmeridgian of the French 

 Jura, is less elongate. Nucula ornati Quenstedt (1851 : 528, pi. 44, fig. 7), which, if 

 Quenstedt's conception of the species is accepted, ranges in Europe from the Upper 

 Bajocian to the Oxfordian, has a slightly more prominent umbo. De Loriol's types 

 of N. bellozanensis were from the Lower Kimmeridgian of northern France. 



I follow Van de Poel (1955) in regarding Palaeonucula as a subgenus of Nuculoma 

 rather than of Nucula. 



Family NUCULANIDAE 



Genus NUCULANA Link 1807 



Subgenus DACRYOMYA Agassiz 1840 



Nuculana (Dacryomya) thompsoni sp. nov. 

 PL 1, figs. 4a, b, c 



Specific name. After Mr. A. O. Thompson, of the Geological Survey of Kenya, 

 collector of the holotype. 



Diagnosis. Small (length of holotype 8-6 mm.), pyriform, height two-thirds of 

 length ; gibbose ; with strongly opisthogyrous, submedian umbones and a short 

 posterior rostrum the narrow extremity of which is slightly below mid-height. 

 Postero-dorsal outline strongly concave ; escutcheon broad, cordate, well impressed, 

 bordered by umbonal ridges. Antero-dorsal outline and anterior and antero-ven- 

 tral margins forming an uninterrupted, parabolic curve ; posterior end of ventral 

 margin almost straight. Surface, except for the smooth escutcheon, ornamented 

 with regular concentric threads, the tops of which are about 0-2 mm. apart. 



Holotype. No. LL. 35000. The only specimen. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. Nuculana zieteni (Brauns) (1871 : 373) (non d'Orbigny sp.), Middle 

 Lias of Europe, is less gibbose and has its posterior rostrum accentuated by a sinus 

 of the ventral margin. The type species of Dacryomya, Nuculana lacryma (J. de C. 

 Sowerby) (1824a : 119, pi. 476, fig. 3), Bathonian of Europe and Asia, is less gibbose 

 and has a more elongate rostrum. In Nuculana gutta (Miinster) (= Nucula muc- 

 ronata Goldfuss 1837, pi- I2 5» n g s - 9&-d, non Sowerby), also known as N. diana 

 (d'Orbigny), Toarcian and Aalenian of Europe, the postero-dorsal profile is less 

 strongly concave and the rostrum less well defined. 



