i 4 2 JURASSIC BIVALVIA AND GASTROPODA 



vergence. In the Triassic genus Diplochilus Woehrmann, which also has two peri- 

 pheral carinae, the aspect of the ornament of the shell is quite different. In Dimor- 

 ■photectus Cossmann, also founded on a Triassic species, the very short columellar lip 

 has a prominent median fold. 



Africoconulus kenyanus sp. nov. 

 PI. 30, figs, ga, b, c 



Diagnosis. Rather small (height of largest specimen 14 mm.), trochiform, with 

 well elevated, slightly coeloconoid spire ; diameter four-fifths of height ; aperture 

 occupying about two-fifths of total height. Spire whorls with a prominent carina 

 situated at lower third of their height and bearing prickly tubercles; above the carina 

 are two spiral rows of smaller tubercles coinciding with angulations of the surface, 

 the upper angulation bordering a narrow sutural ledge. Margin of base formed by 

 a second carina which continues the line of the suture ; this carina is slightly less 

 prominent than the one above it and bears smaller and more numerous tubercles 

 than those on the upper one. The base, which is very little extended, is flattened- 

 convex adaxially and is slightly excavated but not umbilicate mesially ; it bears a 

 few unevenly distributed spiral cords. In addition, the whole surface of the shell 

 bears raised collabral threads which are well separated in some specimens ; threads 

 slightly prosocline above main carina and more strongly so below it, while on the base 

 some become strengthened adaxially to form transverse riblets. Apertural margin 

 imperfect in all specimens. 



Holotype and paratypes. Nos. GG.10250 and GG.10251-57 respectively, 

 eight specimens in all. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. This species is clearly congeneric with Africoconulus spinatus (Dubar), 

 type species of the new genus, but is much smaller and its upper carina has not the 

 prominent spines which are present in that species. 



Subfamily ANGARIINAE Thiele 1924 



Genus CHRYSOSTOMA Swainson 1840 



Chrysostoma staffi Dietrich 



PI. 24, figs. la-c 



i<>i4. Chrysostoma Staffi Dietrich : 122, pi. 11, fig. 6. 



Material. One specimen (no. G. 48567). 



Locality and horizon. " Ditch 2x ", Tendaguru, Tanganyika ; just above top 

 of lower " Trigonia smeei " Bed, i.e. Upper Kimmeridgian (cf. Parkinson 1930, fig. 3, 

 showing horizons near Tendaguru hill). 



