174 JURASSIC BIVALVIA AND GASTROPODA 



Family AKERIDAE Cossmann 1895 



Genus AKERA Muller 1776 



Akera tanganyicensis sp. nov. 

 PI. 29, figs. 5a, b 



Diagnosis. Of medium size (height of holotype 27-5 mm.), cylindrical, involute, 

 with flattened spire ; maximum diameter about three-fifths of height in holotype 

 (in which specimen, however, it is probably increased a little by crushing). Sutures 

 impressed. Sides of last whorl very feebly convex and diverging slightly in an 

 abapical direction as far as the periphery of the base, which lies at about the lower 

 third of the height of the shell, and below which the outline of the base is very feebly 

 convex. Aperture of moderate breadth above, where the inner lip is formed by the 

 steep face of the previous whorl, broadening below, where the inner lip recedes to the 

 columella. Outer lip vertical, curving back to a slight extent at its upper end, to 

 meet the suture ; basal margin of aperture forming an even curve ; columellar lip 

 vertical, short. 



Holotype. No. GG. 10332. The only specimen. 



Locality and horizon. Along Mbaru stream, 1 mile N.W. of Mbinga, Tangan- 

 yika ; Callovian. 



Remarks. This form seems to be congeneric with a series of Jurassic species 

 which Cossmann (18966 : 127-131) includes in Acera [better, Akera], a genus origin- 

 ally founded on Recent forms. In A. mediojurensis Cossmann (18966 : 128, pi. 6, 

 figs. 8, 9), from the Callovian and Lower Oxfordian of France, the side of the last 

 whorl is more strongly convex and the shell is slightly broader in proportion to its 

 height than in the species now described. In A. truncata (Lennier), from the Kim- 

 meridgian of France, the shell, as figured by Cossmann (18966 : 130, pi. 6, figs. 13, 

 14), is even closer to the present form in shape, but is slightly more slender. 



v list of fossil localities, with species collected at each 

 Localities in S.E. Tanganyika 



Tendaguru : Tingutitinguti creek, S.W. of Tendaguru hill ; Upper Kimmeridgian, 

 " Trigonia smeei " Bed. 



Cucullaea sp., Modiolus bipartitus (J. Sowerby), Mytilus (Falcimytilus) dietrichi 

 sp. nov., Lithophaga suboblonga Dietrich, Gervillella aviculoides (J. Sowerby), 

 M eleagrinella radiata (Trautschold), Lima, (Plagiostoma) sp., Lima (Acesta) 

 cutleri sp. nov., Liostrea dubiensis (Contejean), Trigonia (Indotrigonia) smeei 

 auct., Hippopodium quenstedti (Dietrich), Astarte sp., Opis sp., Lucina sp., 

 Mactromya sp., Protocardia schencki Muller, Protocardia {Tendagurium) pro- 

 pebanneiana (Dietrich), Eomiodon (Africomiodon) cutleri sp. nov., Symmetro- 

 capulus ? sp., Pseudomelania (Oonia) dietrichi sp. nov., Ampullospira ? sp., 

 Globularia sp. 



