438 CEETACEOUS 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. quadricostataj 

 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^=^g7'i/pha;atoJ ; 

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

 ribs. The difi'erent 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 qnadricostcda, 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. (equlcostata 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 cpunquecostcda, though 

 certain varieties may be locally constant. 



LocaUties. — North of Odium, Cullapaudy, Moraviatoor, Ootatoor, south of 

 Puravoy, (Ootat. group) ; south-east of Permapolliam, east and north-east of 

 Anapaudy ; south of Scrdamungalum, (Trichinopoly group) ; east and west of 

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



Fonnattoiis. — Ootatoor, Trichinopoly, and Arrialoor groups. 



2. VoLA L^vis, Brouet, PL XXXI, Figs. 7-8. 



1824. Janira (? Neithea) Ictvis, Drouet, teste Pictet et Campiche, Pal. Suiss., Vm" ser., 4nio part., p. 252. 

 1843. Janira phaseola, apud d'Orbign}', Pal. fraiKj. terr. cret., iii, p. 635, pi. 411, figs. 6-9 ; eadem axii 



Keitliea phaseola auctorum, non eadem Lam. 

 1846. Pecten dec'qnens, Reuss, Bohm. Kveidef, pt. ii, p. 31, pi. 45, fig. 3. 

 1808. Pecten phaseolus, apud Giimbel, Abhandl. math. Ph. Klasse, Ba3-er. Al;ad. Wissensch., x, p. 564. 



Vola testa late sxdi-ovata, crassula, apice angnstata, paidulum obliqua, valva 

 dextra convexa, radiatim suh-costata, costis patdultim convexiusculis, latis, cequalibus, 

 Ibie'is hnpressis disjuuclis ; valca sinistra ^;/««rt, radiatim costata, costis angustis. 



