OP SOUTHERN INDIA. 169 



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

 (? Stjb-genus Dosiniopsis, Conrad, 1801), (vide p. 151). 

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



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



„ ? „ Uneolata, ,, „ „ p. 57, „ upper „ 



1839. ? Ci/therea plana, Goldfuss, Petr. Gei-manije, pt. ii, p. 138, pi. 148, fig. 4. 



1843. ? Venus plana, Sowerby, d'Orbiguy, Pal. frani;. terr. eret., vol. iii, p. 447, pi. 38G, figs. 1-3. 



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



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



1867. Venus plana. Sow., Gueranger, Albiuu iialeont. de la Sartbe, pi. xvii, fig. 11. 



Cyth. testa oblouga, inaiquilateraU, antice rotundata, moderate producta, postice 

 sidj-truncata, dedioitate superior'i antica paulo excavata, postica longiore ac con- 

 vexluscula ad term'uiationem anticam rotundata, ad posticam subtrnncata ; mnbonibus 

 prominulis, antice verms paulo incurvis ; valvis moderate convexis, seu applanatis, 

 strils concentricis incrementi tenuibus ac alteris crassioribus instructis ; lunula tonga, 

 cordiforml, paululum excavata seu convexvuscida, linea impressa tenui circumscripta ; 

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

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

 in valva sinistra sitce congruente. 



Length of largest specimen ... ... ... 66 m. m. 



Height „ „ ... ... ... 56 ., 



Thickness „ „ ... ... ... 21 „ 



Height : length ... ... ... 084 to O'Ol 



Thickness : height ... ... ... 0-37 to O'SO 



The form of tliis shell entirely agrees with that of the recent Cgtherece ; it is 

 generally rather less inflated than these, but besides the usual striae 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 svispect that Sowerby's V. Uneolata 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 Cyth. 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 



