314 CEETACEOUS PELECYPODA 



eamlata, Kg. Fraas also describes and figures (1. cit.^ p. 237, pi. iv, fig". 17), a ^^ T. distans^ 

 Conr./'' but does not say whether the species is the same as Coquand"'s distans from Algier, The 

 figures of both show a great similarity, but in the Palsestine form the median areal rib appears to 

 be absent. 



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

 orientalisy semiculta, minutaj and crenifera, 



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

 a. Group, — Scaphoidea, 



1. Trigonia scabra, Lam., PI. XY, Eigs. 24-26, and PI. XYI, Eigs. 35-40. 



1819. Trigonia scahra, Lam., An. sans vert., vol. vi, p. 63. 



1846. „ aliformis, Park, apud Forbes, Trans. Geol. See, Lond., vii, p. 151, non idem, Park. 



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



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



Trig, testa etongatim suh-trigona, valde ina>quilaterali, moderate inflata, timbo- 

 nibus postice versus paulo incurvis, suh-anterioribus, postice producta, attemiata et 

 ad terminationem anguste et oblique sub-truncata, antice rotundata, margine inferiori 

 fere uniforme cm^vato, marg. areali subrecto aut paululum concavo, costis 16-24 con- 

 centincis paulo curvatis, tuberculis acutis coronatis, antice sub-obsoletis, ornata • area 

 transversaliter costulis nume^^osis sub-spinulis, terminalibus cum costis lateralibus 

 nonnunquam angulum acutum formantibus, nonnunquam sub-obsoletis notata sulco 

 longitudinalij haud prof undo, sub-mediano divisa. 



The ornamentation of the 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 

 young 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 Porbes with Parkinson's 

 aliformis, but Porbes 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 limbata, 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 limbata 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.— Ne^v Anapaudy, Koloture, Serdamungalum, Coonum and Shuta- 

 mungalum ; North of Karapaudy. 



Formations. — Trichinopoly and Arrialoor groups. 



