Nigerian Eocene Mollusca. 87 



terminal. Left valve with a strongly conical tooth in front moderately distant 

 from anterior cardinal ; cardinal teeth divergent, coalescent above, lamelliform, 

 the central thick and robust, postero-lateral tooth lamelliform, obliquely curved 

 and quite near to the middle cardinal. Right valve with a front socket to 

 receive anterior tooth of opposing valve, a pair of closely situated, unequal 

 cardinal teeth with flattened parallel inner surfaces, anterior smallest, postero- 

 lateral tooth thick, obliquely lamelliform, and elongately furrowed. 



DIMENSIONS. 



Height 38 millimetres. 



Length ... 36 



Diameter (closed valves) ... ... ... 28 



REMARKS. This species is related to Cytherea incrassata of James 

 Sowerby, the type of Cossmann's Cordiopsis, although it undoubtedly belongs 

 to Sinodia of the late Jukes-Browne, 1 which was founded on Reeve's Dosinia 

 trigona from Recent Seas (Indian Ocean). Some perceptible differences 

 separate our shell from the Sowerbian species. In form it possesses the 

 trigonal and ventricose aspect of the recent shell as opposed to the more 

 oval contour of C. incrassata, whose valves are moreover relatively less deep, 

 more narrowly lunuled, and with only a single obtuse angulation to the 

 posterior region. The double angulation of the posterior region of the 

 Nigerian shell is important from the specific point of view especially, as it 

 forms a good distinguishing feature in support of recognising it as a new form. 

 The dentition generally agrees with that of Sinodia, Cordiopsis, and Dosinia. 

 From the latter genus, it differs in contour, as also in its superficial lunule, 

 and in possessing a shorter, less ascending, and less acuminate pallial sinus. 

 From Cordiopsis, the shape, again, separates it as well as the more ventricose 

 valves ; while the possession of an obtusely angulate posterior region enclosing 

 the elongately-shallow escutcheon distinguishes it from Sinodia. The shell, 

 however, so closely approximates in other characters to the last named genus, 

 that there can be no hesitation in regarding the new species as one of its 

 members. The obtusely carinated character of the posterior region is so 

 important that it must be regarded as an additional feature in the diagnosis 

 of Sinodia, its presence connecting it with the Meretrix shells of the 



1 On the Genera of Veneridae represented in the Cretaceous and Older Tertiary Deposits : Proc. 

 Mai. Soc., London, 1908, Vol. 8, pi. 6, p. 151. 



