150 JURASSIC BIVALVIA AND GASTROPODA 



Pseudomelania (Oonia) conica (Morris & Lycett) 

 PI. 25, figs. 2a, b, c 



1 85 1. Phasianella conica Morris & Lycett : 74, pi. n, figs. 30, 30a. 



1851. Phasianella acutinscula Morris & Lycett : 75, pi. 9, fig. 2 ; pi. 11, figs. 28, 28a (non 



Lycett 1850). 

 1885. Phasianella acutinscula Morris & Lycett : Cossmann : 253, pi. 9, fig. 18 ; pi. 17, figs. 



22, 23. 

 1900. Phasianella ? acutiuscula Morris & Lycett ; Cossmann : 571, pi. 17, fig. 19. 

 19076. Phasianella ? acutiuscula Morris & Lycett ; Cossmann : 253, pi. 7, fig. 5. 



Material. One specimen (no. GG. 10463). 



Locality and horizon. 2 miles W. of Tengeni (village on Pangani river), in 

 Mbuzi Mkubwa stream, Tanganyika ; Bathonian (?). 



Remarks. The specimen, which is 21-5 mm. high, agrees well with some speci- 

 mens from the Great Oolite of England, although it is slightly more slender than those 

 figured by Morris and Lycett. The sutures are flush and the spire is slightly 

 cyrtoconoid. Another Bathonian species, P. (0.) variata (Lycett 1863 : 104, pi. 45, 

 figs. 28, 28a, b), especially as figured by Cossmann (1885 : 255, pi. 4, fig. 52 : pi. 11, 

 fig. 17), is also of much the same proportions as the shell now recorded, but its sutures 

 are more impressed and its base is less extended. 



Pseudomelania (Oonia) dietrichi sp. nov. 

 PL 24, figs. 6a, b 



1914. Pseudomelania (Oonia) aff. Sancti Antonii (Struckmann) ; Dietrich : 129, pi. 11, figs. 

 ija-c. 



Diagnosis. Shell of medium size (height of holotype 34 mm.), of moderate acute- 

 ness (spire angle about 30 °) ; aperture occupying about three-sevenths of total 

 height. Whorls strongly and evenly convex, their mean height equal to about one- 

 half of their diameter. Ornament consisting of faint spiral striae together with 

 growth rugae which are strongly pronounced on the last whorl and are slightly arched, 

 with a backward-facing convexity. 



Holotype and paratypes. Nos. G. 48028 and G. 48021-27 respectively, eight 

 specimens in all. 



Locality and horizon. Tingutitinguti creek, Tendaguru, Tanganyika ; Upper 

 Kimmeridgian, " Trigonia smeei " Bed. 



Remarks. A search through the literature has confirmed Dietrich's conclusion 

 that the most closely comparable species previously described is Chemnitzia Sancti 

 Antonii Struckmann (1878 : no, pi. 7, figs. 2a, 6,3), from the Kimmeridgian of Ahlem, 

 near Hanover. In the species in question, however, the shell is slightly more acute 

 than in the Tendaguru shell and a fine reticulate ornament is present, in which the 

 spiral threads are slightly more prominent than the collabral ones, whereas in the 

 East African form the spiral lines are scarcely visible to the unaided eye and much 



