7t JURASSIC BIVALVIA AND GASTROPODA 



1930. Exogyra nana (J. Sowerby) ; Weir : 85, pi. 10, figs. 27-29. 

 1052. Exogyra nana (J. Sowerby) ; Cox : 92, pi. 10, figs. 2-4. 



Material. Several specimens. 



Localities and horizons. Ogar Wein and Tifo, N.E. Kenya ; Oxfordian, 

 Golberobe Beds. z\ miles S.W. of Rahmu, N.E. Kenya ; Oxfordian, Rahmu Shales. 

 Hereri river crossing, 3 miles S. of Melka Kunha, N.E. Kenya ; Kimmeridgian, 

 Hereri Shales. Kiwate-Mkange track, 5 miles S.S.E. of Mkange, Bagamoyo hinter- 

 land, Tanganyika ; Oxfordian or Kimmeridgian. Kindope valley, near Tendaguru, 

 Tanganyika ; Upper Kimmeridgian, Nerinella Bed. 



Remarks. Most of the specimens are irregular in form, but some from the Rahmu 

 Shales are characterized by their regularly lunate outline, recalling that of the larger 

 form E. foitrtaiti Stefanini (see Cox 1935a : 174, pi. 17, figs. 14a, b). Occasional 

 European specimens of E. nana (e.g. de Loriol 1872, pi. 24, figs. 12, 12a, b) are, how- 

 ever, similar in shape. 



Superfamily TRIGONIACEA 



Family TRIGONIIDAE Lamarck 1819 



Genus TRIGONIA Bruguiere 1789 



Trigonia costata Parkinson 

 PL 11, figs. 2a, b 



1811. Trigonia costata Parkinson : 175, pi. 12, fig. 4. 



1875. Trigonia costata Sowerby ; Lycett : 147, pi. 29, figs. 5-10. 



1932. Lvriodon costatum (Sowerby) ; Lebkiichner : 101, pi. 15, fig. 9 ; pi. 16, fig. 3. 



Material. One specimen (no. LL.35104), ex B.P. Coll. 



Locality and horizon. Magole, 5 miles N.W. of Kidugallo, Tanganyika ; 

 Bajocian. 



Remarks. This small specimen, about 18 mm. long and 16 mm. high, appears 

 to be referable to the true T. costata, a Bajocian species which has been much mis- 

 interpreted. The angular concentric ribs, 16 in number, almost touch the marginal 

 carina in the right valve, but are separated from it in the left by an ante-carinal 

 depression which is fairly narrow, although broader than in the new species T. kenti, 

 described below. The posterior area bears a relatively prominent nodose rib the 

 position of which is anterior to median. Between this rib and the marginal carina 

 is a single nodose thread and on its posterior side are three other threads, irregularly 

 arranged. The escutcheon has a few transverse wrinkles. These features are similar 

 to those of English specimens of T. costata which have reached the same stage of 

 growth. Previous records of T. costata from East Africa are from post-Bajocian 

 beds and are to be rejected. 



