. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS TRIGONIIDAE FROM THE BRENTON FORMATION 61 terminate along the anterior margin of the shell. The flanks are ornamented with very fine growth striae which cut obhquely across the ribbing. The teeth are typically trigoniid. The central tooth of the left valve is very prominent and robust, while the anterior tooth is weakly developed, thin, lath-like, and is directed almost vertically downwards. The prominent anterior tooth of the right valve is directed vertically downwards, and is supported
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS TRIGONIIDAE FROM THE BRENTON FORMATION 61 terminate along the anterior margin of the shell. The flanks are ornamented with very fine growth striae which cut obhquely across the ribbing. The teeth are typically trigoniid. The central tooth of the left valve is very prominent and robust, while the anterior tooth is weakly developed, thin, lath-like, and is directed almost vertically downwards. The prominent anterior tooth of the right valve is directed vertically downwards, and is supported on a thickened ledge of shell. The posterior tooth is weakly developed, lath-hke, and meets the anterior tooth at an angle of about 60°. Discussion This species most closely approaches Steinmanella mamillata (Kitchin) (Fig. 9) from the Oomia Group of Kutch, southern India. Kitchin's (1903) species differs from S. kensleyi, however, in having a more quadrate outline, while most of the flank ribs terminate along the ventral margin of the shell. This distinction is confirmed by topotype material in the British Museum (Natural History). The differences are not great, but, in view of the greater age of the Indian species (Uppermost Tithonian or Berriasian), they are considered sufficient for specific separation. The Brenton species is a close homoeomorph of the Aptian 'Trigonia' bronni Agassiz, as is indicated by a specimen in the collections of the South African Museum (D1622) (Fig. 10), from Perte-du-Rhone, France. The French species has, however, a more convex anterior margin, twice as many tubercles in the marginal carina than there are flank ribs (in S. kensleyi they are almost equal), a more prominent median longitudinal furrow, and lacks the coarse tuberculation of the escutcheon seen in S. kensleyi. Moreover, the transverse. Fig. 9. Steinmanella {Steinmanella) mamillata (Kitchin). The holotype from the uppermost Tithonian or Berriasian of southern India. After Kitchin (1903
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
