132 JURASSIC BIVALVIA AND GASTROPODA 



Pleuromya calceiformis (Phillips) 

 PI. 20, fig. 9 



1829. Mya calceiformis Phillips : 155, pi. 11, fig. 3. 



1863. Myacites calceiformis (Phil.); Lycett : 80, pi. 42, figs. 1, 1a. 



1934a. Pleuromya calceiformis (Phil.) ; Arkell : 324, pi. 44, figs. 12, 12a. 



Material. One specimen (no. LL.35158), ex B.P. Coll. 



Locality and horizon. Mandawa-Lonji creek traverse, Mandawa area, Tangan- 

 yika ; Upper Oxfordian. 



Remarks. The specimen now recorded is in every way typical of the species. 

 This has not been recorded previously from East Africa or from anywhere in the 

 Indian Ocean region. 



Family CERATOMYIDAE Arkell 1934 

 Genus CERATOMYA Sandberger 1864 



Ceratomya tanganyicensis sp. no v. 



PI. 21, figs. la, b, c 



Diagnosis. Of medium size (length 41 mm.), ovate with a trigonal tendency, 

 moderately inequilateral, height four-fifths of length, beaks at about anterior third 

 of length ; shell well inflated mesially, somewhat compressed posteriorly. Umbones 

 very broadly rounded, not prominent, well incurved to the beak, which was apparent- 

 ly not strongly prosogyrous for the genus, but is obscured in the only available speci- 

 men. Postero-dorsal outline very feebly convex, rather steeply sloping, joining the 

 fairly sharply rounded posterior margin in an even curve ; ventral margin very 

 strongly convex anteriorly, almost angular posteriorly, where it bends up to the 

 narrowly rounded anterior end of the shell ; antero-dorsal outline very feebly con- 

 cave. Ornament of numerous narrow, rounded, subequal concentric ribs, which 

 number rather more than 20 to the cm. 



Holotype. No. LL.35159. The only specimen. 



Locality and horizon. Lihimaliao creek, at a point near Mbaru creek, Man- 

 dawa area, Tanganyika ; Bajocian (?), Pindiro Shales. 



Remarks. The closeness of the concentric ribbing distinguishes this from all other 

 post-Liassic species of the genus. In C. madagascariensis (Thevenin) (19086 : 28, 

 pi. 3, figs. 9, 9a), from the Upper Lias of Madagascar, the shell is higher and less 

 elongated. 



Ceratomya concentrica (J. de C. Sowerby) 

 PI. 20, fig. 7 



1825a. Isocardia concentrica J. de C. Sowerby : 147, pi. 491, fig. 1. 



1855. Isocardia concentrica Sowerby ; Morris & Lycett : 108, pi. 10, figs. 3a, b (non pi. 15, 

 figs. ia, b). 



