314 CllETACEOUS PELECYPODA 



candata, Ag'. Fraas also describes and figures (1. eit., p. 237, \A. iv, fig. 17), a " T. disfann. 

 Com-.," but does not say whether the species is the same as Coquand's didans from Algier. The 

 fio-iires of both show a great similarity, but in the Palajstine form the median areal rib appears to 

 be absent. 



80-85. — The following species occur in Southern India: T. scabra, Lam., tuberctdifera, indica, 

 orientalis, semiciiUa, minuta, and cremfera. 



TEIGONIA, Brug., 1789, (see p. 310). 

 a. Group, — Scaphoidea. 



1. Trigonia scabra, Lam., PI. XV, Figs. 24-26, and PI. XVI, Figs. 35-40. 



1819. Tric/onia scabra, Lam., An. sans vert., vol. vi, p. 63. 



1846. „ aliformis. Park, apud Forbes, Trans. Geol. Soc, Lond., vii, p. 1.51, non idem. Park. 



1850. „ limhata, d'Orb., Prod. II, p. 240, ex parte, idem Gabb, Zittcl, et auctorum. 



1865. „ scabra, Lam., apud Zittel, Denk. Akad., Wien, xxiv, pt. ii, p. 161, cum syn. 



Trig, testa elongatlm sub-trlgona, valde iiKequilaterall, moderate inflata, umbo- 

 n'lbns postice versus paulo incurvis, suh-anterlorihus, postice producta, attenuata et 

 ad termmatlonem anguste et oblique sub-truncata, aritice rotundata, margine inferiori 

 fere uniforme curvato, marg. areali subrecto aut paululum concavo, costis 16-24 con- 

 centricis paido ciirvatis, tuberculis acutis coronatis, antice sub-obsoletis, ornata ; area 

 transversaliter costuUs numerosis sub-spinnlis, termlnalibtis cum costis laterallbus 

 nonniinquam augidnm acutmn formantibus, nonnunquam sub-obsoletls notata, sulco 

 longUudlnall, hand pit'of undo, siib-mediano dlvlsa. 



The ornamentatiou of tlie surface is subject to great variation. When the 

 shell is well preserved the ribs are provided with very distinct spinulose tubercles 

 and separated by deep interspaces which are broader than the ribs themselves ; in 

 voung specimens this is particularly apparent. When, however, the surface of 

 the valves becomes worn off the tubercles often quite disappear, the ribs are then 

 smooth and apparently broader than the interspaces. All these variations are 

 amply illustrated in the figures cited above. 



Our South. Indian form had first been identified by Forbes with Parkinson's 

 aliformis, but Forbes never saw a perfect specimen of the Indian form, and the 

 anterior parts of both the species are very easily mistaken, the one for that of the 

 other. D'Orbigny, apparently acting more on geological than on conchological 

 evidence, considered the Indian form identical with his llmbata, and this state- 

 ment has been accepted as correct by subsequent writers. Zittel refers to it as if 

 there were not the least doubt about it. But an examination of a large series of 

 the Indian fossils proved them to belong to scabra of Lamarck, as distinguished 

 from llmbata by more straight, more numerously and equally tuberculated ribs and 

 less concave areal margin. Both species are, however, very closely allied, and it is 

 often far from an easy task to separate one from the other. 



Localities. — Near Anapaudy, Koloture, Serdamungalum, Coonum and Shuta- 

 mungalum ; North of Karapaudy. 



Formations. — Trichinopoly and Arrialoor groups. 



