154 JURASSIC BIVALVIA AND GASTROPODA 



Localities and horizon. Near site of Mandawa well no. i, Tanganyika (type- 

 locality). Mandawa well no. 6, Tanganyika, at depths 58-60 feet, 60-62 feet, 62-64 

 feet, 64-66 feet, 66-68 feet. Lihimaliao creek, at a point near Mbaru creek, Man- 

 dawa area, Tanganyika (a specimen preserved in matrix adherent to a crushed speci- 

 men of Protocardia bipi). All Bajocian (?), 



Remarks. There has been some difference of opinion as to the distinction be- 

 tween Coelostylina and Omphaloptycha , a genus founded by von Ammon two years 

 earlier. According to the criteria accepted by Cossmann (1909 : 47), the species 

 now described might appear better referable to Omphaloptycha, its ovate-conical form 

 and the feeble convexity of its whorls distinguishing it from the type-species of 

 Coelostylina. Nevertheless, in a later work Cossmann (1913& : 211-218, pi. 15) 

 refers a number of species, very much like the African shell, to Coelostylina. I think 

 it undesirable to separate this form generically from C. kidugalloensis sp. nov., des- 

 cribed above, and I therefore also include it in Coelostylina. It differs from C. 

 kidugalloensis in its less convex whorls and its more extended and relatively narrower 

 aperture. 



Superfamily LOXONEMATACEA 

 Family ZYGOPLEURIDAE Wenz 1938 

 Genus ZYGOPLEURA Koken 1892 



Zygopleura mandawaensis sp. nov. 

 PL 25, figs. 3a, b, 11 



Diagnosis. Shell rather small (height of largest specimen about 12 mm. when 

 complete), acute ; spire angle abut 15°. Protoconch finely pointed. Whorls with 

 an imbricate appearance, due to presence of an obtuse angulation at about the lower 

 quarter of their height, above which their outline is flattened ; the angulation forms 

 the periphery of the last whorl. Ornament consisting of strong, rounded collabral 

 costae separated by intervals of about the same width ; in some specimens the costae 

 are opisthocyrt for the whole of their exposed length, while in others they are para- 

 sigmoid, with the part above the angulation opisthocyrt and the part below proso- 

 cline. On the penultimate or the last whorl the costae fade away, so that the surface 

 bears only collabral threads or rugae. Base smooth, feebly convex to almost flat in 

 outline. Outer lip with broad sinus corresponding to opisthocyrt part of costae. 



Holotype and paratypes. Holotype, no. GG.10287 (ex B.P. Coll.), a specimen 

 associated with the holotype of Ceratomya tanganyicensis, sp. nov. There are several 

 paratypes, including nos. GG. 10288-89, none complete. 



Localities and horizon. Lihimaliao creek traverse, Mandawa area, Tangan- 

 yika (type-locality). Mandawa well no. 6, Tanganyika, at the following depths : 

 58-60 feet, 60-62 feet, 62-64 feet, 64-66 feet. Near site of Mandawa well no. 1. 

 All Bajocian (?). 



Remarks. The Middle Jurassic species of Zygopleura so far described are relatively 

 large forms, 50-100 mm. in height, and it is necessary to turn to the Lias to find any 



