8o JURASSIC BIVALVIA AND GASTROPODA 



Locality and horizon. Just W. of Mabokweni, 4 miles N.W. of Tanga, Tangan- 

 yika ; Kimmeridgian. 



Remarks. There is no described Myophorella with which this species could be 

 confused. In M. kutchensis (Kitchin) (1903 : 84, pi. 8, figs. 7-9) the umbo is less 

 prominent and the costae are broken up into irregularly distributed tubercles on the 

 anterior part of the flank. 



Myophorella kiwawaensis sp. no v. 

 PL 12, figs. 2a, b 



Diagnosis. Small, ovate, almost orbicular, length (c. 16 mm.) only slightly 

 exceeding height. Umbones not prominent, at anterior third of length. Anterior 

 and ventral margins forming an even curve of strong convexity ; posterior margin 

 relatively long, erect. Marginal carina gently curved, obtusely angular, nodose ; 

 escutcheon carina nodose. Posterior area short, moderately broad, without median 

 groove, and bearing closely arranged transverse threads. Flank with rather deli- 

 cate nodose costae, those near posterior end straight and vertical, middle ones well 

 curved. 



Holotype and paratypes. Holotype, no. LL.35110, also three paratypes, 

 including no. LL.35111 ; all ex B.P. Coll. 



Locality and horizon. Kiwawa stream, 2400 yards S.E. of Mitekera survey 

 beacon, northern Mandawa area, Tanganyika ; Upper Kimmeridgian. 



Remarks. The absence of a radial groove on the posterior area distinguishes this 

 species from young specimens of Myophorella striata (Miller) and of related Inferior 

 Oolite species. 



Genus LAEVITRIGONIA Lebkiichner 1932 



Laevitrigonia dwanikana sp. nov. 

 PL 12, fig. 5 



Diagnosis. Shell of medium size (length 35 mm.), ovate, rounded posteriorly ; 

 length not greatly exceeding height. Umbo not prominent, situated at about 

 anterior third of length ; ventral margin strongly and symmetrically convex. 

 Marginal carina an obscure ridge ; posterior area convex, forming a wide angle with 

 the flank ; no ante-carinal depression. Anterior part of flank ornamented with 

 broad, depressed rounded ribs, some split up into irregular nodes by transverse 

 furrows, separated by much narrower intervals. In earlier stages of growth the 

 ribs bend up to the marginal carina, but in later stages they end half-way to the 

 carina, leaving the rest of the flank smooth. Posterior area apparently without 

 ornament (but rather eroded in holotype). 



Holotype. No. L. 52692 ; the only specimen. 



Locality and horizon. Dwanika river, Tendaguru, Tanganyika ; Upper 

 Kimmeridgian, " Trigonia smeei " Bed. 



