438 CRETACEOUS PELECYPODA 



all three divisions of the South Indian Cretaceous deposits. Again, some other 

 specimens have between the first and second, or between the second and third, 

 anterior larger ribs four intermediate ones ; very rarely is it the case that only 

 two intermediate ribs occur in one or the other of the interspaces between the larger 

 ribs. I only observed it in a few specimens from Odium (see fig. 8, pi. xxxvii) ; 

 they are also all of large size. Three intermediate sub-equal ribs fV, qiiadricostata) 

 are only met with in some small specimens from Arrialoor and Shillagoody. 



I have compared a very large series of specimens from various localities and 

 formations, and I am confident that the Indian shell does not admit any such dis- 

 tinction, as has been proposed for V, quinquecostata and quadricostata f=gryph(Eata) ; 

 the former said to possess always four and the latter always three intermediate 

 ribs. The different variations are not restricted either to particular localities, or to 

 distinct formations ; they occur without any rule one among the other. The only 

 thing which could be said is, that specimens from the Ootatoor group have more 

 commonly four and those from the Arrialoor group more commonly three inter- 

 mediate ribs. I also could find no perceptible difference in the form and striation 

 of the ears of the various Indian specimens. The state of preservation has a 

 great deal to do with the relative size of the ribs and is often very misleading. 



I do not wish to pronounce a certain opinion as to the identity of V. quinque- 

 and quadricostata, but I cannot help doubting their specific distinction. The 

 support which d'Orbigny gave to his opinion, by placing the one shell in the 

 Turonien and the other in the Senonien, has been long ago disproved : such geolo- 

 gical restriction does not exist ; both forms occur from the Tourtia and Cenomanien 

 up into the upper beds of the white chalk. 



I have no specimens of d'Orbigny 's V, cequicostata and alpina to compare, but 

 judging from the observations which I made on the Indian specimens, I doubt 

 that even these two will prove to be distinct species from quinquecostata, though 

 certain varieties may be locally constant. 



Localities, — North of Odium, OuUapaudy, Moraviatoor, Ootatoor, south o^ 

 Puravoy, (Ootat. group) ; south-east of PermapoUiam, east and north-east < ^j 



Anapaudy; south of Serdamungalum, (Trichinopoly group); east and west v.. j 



Arrialoor; south-east of MuUoor, Shillagoody, and Olapaudy (Arrialoor group). 



Formations, — Ootatoor, Trichinopoly, and Arrialoor groups. 



2. VoLA L^vis, Drouet, PL XXXI, Eigs. 7-8. 



1824. Janira (? Neitliea) IcBvis, Drouet, teste Pictet et Campiclie, Pal. Suiss., V^^e ser., 4^6 part., p. 252. 

 1843. Janira pJiaseola, apud d'Orbigny, Pal. fran^. terr. cret., iii, p. 635, pi. 444, figs. 6-9 ; eadem d.v.i 



Neithea pJiaseola auctorum, non eadem Lam. 

 1846. Pecten deci;piens, Eeuss, Bohm. Kreidef, pt. ii, p. 31, pi. 45, fig. 3. 

 1868. Pecten ]phaseolus, apud Giimbel, Abhandl. matb. Pb. Klasse, Bayer. Akad, Wissenscb., x, p. 564. 



Vola testa late sub-ovata, crassula, apice angustata, paululum ohliqua, valva 

 dextra convexa, radiatim sub-costata, costis paululum convexiusculis, latis, cequalibus, 

 lineis impressis disjunctis ; valva sinistra plana, radiatim costata, costis angustis 



