140 JURASSIC BIVALVIA AND GASTROPODA 



Remarks. The genus Rhytidopilus (type-species Patella humbertina Buvignier) 

 was founded by Cossmann (1895 : 143) for the reception of certain rather irregularly 

 conical internal moulds of shells of Mesozoic age with strong growth undulations and 

 a narrow, elevated sector, bordered by furrows, running from the apex to the anterior 

 margin. Pseudorhytidopilus includes patelliform shells which are similar to Rhytido- 

 pilus except that the raised anterior sector is absent. The species most closely com- 

 parable to the one now described is Pseudorhytidopilus arsinoe (d'Orbigny) (figured 

 by Thevenin 1913a, pi. 36, figs. 1,2), from the Callovian of France, but in that species 

 the apex is more elevated and placed in a less anterior position. Its anteriorly 

 pointing and much more forward-placed apex distinguishes the new species from the 

 three European Kimmeridgian species P. banneana (Rollier) (1918 : 11, for Patella 

 humbertina Thurmann & Etallon 1861, pi. 13, fig. 131, non Buvignier), P. castellana 

 (Thurmann & Etallon) (1861, pi. 13, fig. 132), and P. lennieri Cox (i960 : 237, for 

 Helcion castellana Lennier 1872, pi. 8 B, figs. 8, 8a). 



Family SYMMETROCAPULIDAE Wenz 1938 



Genus SYMMETROCAPULUS Dacque 1933 



Symmetrocapulus ? sp. 

 PI. 22, figs. 5a, b 



1914. IPatella (Fissurella ?) sp. ; Dietrich : 116, pi. 11, fig. 4. 



Material. One specimen (no. G. 48031). 



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

 Kimmeridgian, " Trigonia smeei " Bed. 



Remarks. The specimen now recorded is a small, radially ribbed, patelliform 

 shell nearly 9 mm. long. Like the specimens described by Dietrich, as cited above, 

 it has lost its apex, so that its generic affinities are uncertain. The apex was evident- 

 ly situated within the anterior third of the length of the shell, the dorsal profile rising 

 slightly above it posteriorly before curving down to the posterior margin. The 

 numerous radial riblets are unequal in breadth and rather irregularly distributed ; 

 their intervals are, on the average, of about the same width as the riblets. The whole 

 surface, where uneroded, can also be seen to bear fine concentric threads. Dietrich's 

 figure appears to represent a specimen with broader and fewer ribs than the present 

 one, but the species may be the same. Haber (1932 : 249) suggested the reference 

 of Dietrich's form to Symmetrocapulus (then a nomen nudum), but the part of his 

 catalogue in which it would have been listed systematically and possibly given a 

 specific name was never published. 



