OP SOUTHERN INDIA. 437 



ation very much resembles that of Am. cretacenm* Nyst, f= Feet, corneus apud 

 Nilss., non idem Sowerby), the surface being marked with impressed, concentric 

 lines or grooves, about one millimetre distant from each other ; the interspaces 

 are flat and also very finely concentrically striated; at the sides of the valves 

 both striae and grooves generally become indistinct or obsolete. The posterior ear 

 is slightly smaller, and has a very oblique, slightly flexuous, margin ; the anterior 

 is a little larger and more truncate; both are marked with concentric striae of 

 gi'owth. The concentric grooves are traceable also on the inner side of the valves. 



Locality. — Near Arrialoor, in a light grey sandstone. 



Formation. — Ai'rialoor group. 



VOLA, Klein, 1753, (see p. 42G). 



1. VoLA QUINQUECOSTATA, Soiccrbij, PI. XXXI, Figs. 1—6, and PI. XXXVII, 



Pigs. 4—9. 



1814. Pecten q^uinquecostaius, Sowerby, Min. Conch., I, p. 121, pi. 56, figs. 4-8 — idem auetorum. 



1819. Pecien versicostatiis, Lam., An. s. vert., vi, p. 181. 



1843. Janira qiiinquecosfata, d'Orbigny, Pal. franf. terr. cret., iii, p. 632, pi. 444, figs. 1 — 5. 



1846. Pecien quinquecostatus, apud Forbes, Trans., Geol. Soc, Lond., vii, p. 153. 



1847. Janira Fontanieri, d'Orb., Voy. Astrolabe, &o., Paleont., pi. iv, figs. 38 — 40. 



Vola testa ovato sub-trigona, clausa ; valva dextra valde convexa, radiatim costis 

 6 majoribiis, ad marginem 2)Ihs mimisve p^^ojicientibits, 4, 3, aiit rarissime 2, costulis 

 minoribiis, siib-cequalibHS vel incsqtialibus interpositis ornata, declivitate antica et 

 postica striis 4-5 radiantibus notata ; valva sinistra plana aut paulo concava, 

 similariter costata ; titmque striis concentricis, fiUformibus, confertissimis tecta, 

 auriculata, auriculis sub-cequalibus, radiatim striatis, auricula postica pauliilmu 

 majore quam antica. 



In referring a grea number of Indian specimens to this well known European 

 species, it is necessary to state the variations which are to be observed in them 

 and to draw attention to the numerous figures representing them. 



The most characteristic forms of V. quinqnecostata occur in a yellowish soft 

 marly rock south-west of Coonum ; they nearly all possess four intermediate ribs 

 between each larger one, and the two median of the four are again somewhat 

 thicker than the two lateral ones. Exactly similar forms also occur north of 

 Odium, at Ootatoor, and south of Puravoy, south-east of Permapolliam (Trichino- 

 poly group), and near Arrialoor (Arrialoor group), but at all these localities 

 the typical form does not appear so common as some varieties. At Odium, 

 Moraviatoor, and Ootatoor there occur specimens which often grow to a consi- 

 derably larger size than at Coonum, and in these there are, as a rule, only three 

 smaller ribs between each two larger ones, except between the two posterior larger 

 ribs, where there are almost invariably four smaller ribs present. This variety also 

 occurs at Permapolliam, Anapaudy, Serdamungalum, and Arrialoor ; therefore in 



* Coq. et polyp, loss, de terr. ter. de Belgique, 1843, p. 299. 



5p 



