[38 JURASSIC BIVALVIA AND GASTROPODA 



Genus NUMMOCALCAR Cossmann 1896 



Nummocalcar mitoleensis sp. now 



PI. 22. figs. 2a, b, c 



Diagnosis. Of medium size (diameter 24 mm.), discoidal, with a barely pro- 

 truding spire, the apex of which is just visible when the shell is viewed from the side, 

 and with the periphery formed by a smooth, projecting carina at about mid-height. 

 Outer face, above the carina, flat and inclined inwards steeply as far as an angulation 

 which bears well separated, rounded nodes and forms the border of the flat upper face. 

 Base, consisting of all the surface below the carina, slightly concave in profile owing 

 to the presence of a broad swelling, bearing weak, transversely elongated tubercles, 

 on the outer side of a smooth spiral cord which forms the margin of the moderately 

 broad umbilicus. Where not eroded, the base bears weak spiral cords, but any spiral 

 ornament that may have been present above the peripheral carina has been oblitera- 

 ted by erosion. Aperture broader than high, but with its margin not preserved in- 

 tact ; growth-lines visible below the peripheral carina show that the outer lip was 

 strongly prosocline, and had a very broad sinus. 



Holotype. No. GG. 10282, ex B.P. Coll. The only specimen. 



Locality and horizon. Mpilepile stream bed, 1650 yards N.E. of Mitole road 

 junction, northern Mandawa area, Tanganyika ; Upper Kimmeridgian. 



Remarks. This species belongs to a group of Jurassic and Cretaceous forms 

 characterized by a carinate periphery and by tuberculate ornament on both the 

 upper face of the whorls and the base, the tubercles being elongated transversely in 

 some species to form ribs. The Albian species " Solarium " subornatum d'Orbigny 

 (S. ornatum J. de. C Sowerby, non Lea) is a characteristic representative of this group 

 and is clearly congeneric with the form now described. Until a revision of all 

 Mesozoic discoidal and subdiscoidal shells can be carried out, Cossmann is followed 

 in referring the species of this group to Nummocalcar. In the type species of this 

 genus, however, strong transverse ribs on the upper face of the whorls end in promin- 

 ent spines on the peripheral carina. It is uncertain if this genus should be included 

 in the Euomphalidae, where it was placed by Cossmann, or if it should be assigned 

 to the Architectonicidae or possibly to a new family. 



Superfamily PLEUROTOMARIACEA 



Family PLEUROTOMARIIDAE Swainson 1840 



Genus BATHROTOMARIA Cox 1956 



Bathrotomaria aitkeni sp. nov. 

 PL 22, fig. 6 ; PI. 23, figs. la, b 



Specific name. After Dr. W. G. Aitken, lately Director of the Geological 

 Survey of Nyasaland, collector of the type specimens. 



Diagnosis. Large (original height of largest specimen no mm.), trochiform, 



