OP SOUTHERN INDIA. 169 



CYTHEEEA, Lamarck, 1807, (vide p. 150). 

 (? Sub-genus Dosiniopsis, Conrad, 1864), (vide p. 151). 

 1. Cytherea plana, Sowerhy, sp., PI. VII, Eigs. 1-4. 



1812. Venus plana, Sowerby, Min. Concli., vol. i, p. 58, pi. xx, lower figure. 



„ ? „ lineolata, „ „ „ p. 57, „ upper „ 



1839. ? Cytherea plana, Goldfuss, Petr. Germanise, pt. ii, p. 138, pi. 148, fig. 4. 



1843. ? Venus plana, Sowerby, d'Orbigny, Pal. frang. terr. cret., vol. iii, p. 447, pi. 386, figs. 1-3. 



1847. ? V. plana, Sow., Muller, Petr. Aacb. Kreidef., pt. i, p. 25. 



1850. ? Venus suh-plana, d'Orb., Prod, ii, p. 237 — idem, Pictet, Bosquet, &c. 



1867. Venus 'plana. Sow., Gueranger, Album paleont. de la Sartbe, pi. xvii, fig. 11. 



Cyth, testa ohlonga, inceqtiilaterali, antice rotundata, moderate producta, postice 

 suh'truncata, declivitate superiori antica paulo excavata, postica tongiore ac con- 

 vexiusGula ad terminationem anticam rotundata, ad posticam subtrimcata ; umbonibtts 

 prominuUs, antice versus paulo incurvis ; valvis moderate convexis, seu applanatis, 

 striis concentricis incrementi tenuibus ac alteris crassioribus instructis ; lunula longa, 

 cordiformi, paululum excavata seu convexiuscula, tinea impressa tenui circumscripta ; 

 cardo in utraque valva dentibus tribus cardinalibus posticis bifurcatis instructus, dente 

 lunulari in valva dextra tenui margini lumilari parallelo, et excavationi profundce 

 in valva sinistra sitce congruente. 



Lengtb of largest specimen 

 Heigbt „ „ 



Tbickness „ „ 



Heigbt : lengtb 



Tbickness : beigbt 



DO m. m. 

 56 „ 

 21 „ 

 0-84 to 0-91 

 0-37 to 0-50 



The form of this shell entirely agrees with that of the recent Cytherece ; it is 

 generally rather less inflated than these, but besides the usual stri^ of growth there 

 is no other ornamentation present. The convexity, length, height, and thickness 

 are subject to slight variations which are, however, not very considerable. The beaks 

 are rather prominent, close together, and slightly incurved, the upper anterior slope 

 being slightly excavated, the posterior convex and considerably longer than the 

 former ; the posterior end is somewhat narrowly truncated, while the anterior one 

 is rounded and more or less produced. These variations are to be observed equally 

 clearly in our own specimens, as in those from Blackdown, and for this reason 

 I greatly suspect that Sowerby's V, lineolata is not distinct from the present 

 species, as already alluded to (p. 160). The inner edge of the shell is, as usually, 

 smooth, the pallial sinus about as deep as in the recent CytJi. attenuata, Dunk., 

 slightly more angular at the end; the fulcra supporting the ligament are 

 thick and long. The hinge exposes three cardinal teeth of the usual form, 

 the posterior is deeply grooved ; the lunular tooth is thin, and about parallel to 

 the lunular margin, upon which peculiarity Conrad proposes a special sub-genus 

 Dosiniopsis, This seems to me, however, only to indicate a wish to satisfy that 

 author's curious idea, that all the cretaceous species belong to genera distinct 

 from those to which tertiary or recent species are referable. 



-2 T 



