122 JURASSIC BIVALVIA AND GASTROPODA 



Locality and horizons. Mandawa well no. 6, Tanganyika, at depths 46-48 feet 

 (holotype), 48-50 feet, 50-52 feet, 52-54 feet, 54-56 feet, 56-58 feet, 58-60 feet, 

 62-64 f eet > 64-66 feet, 70-72 feet ; Bajocian (?). 



Remarks. In the two French Bajocian species C. aglaia d'Orbigny and C. alimena 

 d'Orbigny (types figured by Thevenin, iqua, pi. 26, figs. 34 and 36, 37 respectively), 

 which may be synonymous with one another, the truncated posterior end of the shell 

 is lower and the concentric ornament less regular than in the new species. 



Corbula tanganyicensis sp. nov. 

 PL 19, figs, ga, b, 12a, b, c, d 



Diagnosis. Rather small (length of largest specimen c. 5 mm.), trigonally ovate, 

 slightly inequilateral, some specimens subrostrate posteriorly, height two-thirds of 

 length, beaks situated between anterior third and middle of length ; very slightly 

 inequivalve, left valve slightly the lower, with its ventral margin overlapped by that 

 of right valve, but scarcely differing from the latter in its moderately strong inflation. 

 In both valves, umbo broadly rounded, well incurved to the rather strongly proso- 

 gyrous beak ; umbonal outline rising well above the straight, gently inclined, and 

 in some specimens relatively short postero-dorsal margin ; ventral margin strongly 

 convex anteriorly, flattened or sinuate posteriorly ; antero-dorsal outline slightly 

 concave, steeply sloping ; anterior margin of varying convexity ; a well-defined, 

 sigmoidal diagonal ridge delimits a concave posterior area. Ornament consisting of 

 fine, regular concentric riblets present on flank but not on posterior area. 



Holotype and paratypes. Holotype, no. LL. 35150 ; several paratypes, in- 

 cluding no. LL.35151. All ex B.P. Coll. 



Locality and horizons. Mandawa well no. 7, Tanganyika, at depths 3760-3770 

 feet and 4510-4520 feet (holotype) ; Bajocian (?). 



Remarks. This species is smaller and slightly more gibbose than C. mandawaen- 

 sis, and also differs in its narrower, commonly rostrate posterior extremity and in its 

 rather coarser concentric ornament. 



Corbula pindiroensis sp. nov. 

 PL 19, figs. 14a, b, c, 15a, b 



Diagnosis. Of medium size for the genus (length of largest specimen c. 13 mm.), 

 trigonally ovate, slightly to moderately inequilateral, not rostrate posteriorly, height 

 about two-thirds of length, beaks at anterior two-fifths to third of length ; rather 

 strongly inflated, apparently sub-equivalve (all specimens, however, have suffered 

 some distortion by compression). In both valves, umbo very broadly rounded, well 

 incurved to the moderately prosogyrous beak ; umbonal outline rising only slightly 

 above the feebly concave postero-dorsal outline, which forms a slightly obtuse angle 

 with the straight, low, slightly oblique posterior margin ; ventral margin of rather 

 strong convexity, straightened and upturned at its posterior end ; anterior margin 



