42 CRETACEOUS PELECYPODA 



(11- perhaps more probably a Cnjptomija, in whicli case it would lie the first species of the genus from 

 uretaceons rocks. 



59-6 i.— Meek (Smiths. Misc. Coll., No. 177,) quotes from North America iV. altpformu, fibrosa, 

 Moreauensis and veniricosa, and Gal)b described N. dolabrceformis (Pal. California, i, ISGl, p, 13.3). 



65.G0. — Two species occur in our South Indian cretaceous deposits, N. muf.ua and detecta, the 

 last of which has some resemblance to Corb. strialida, but its shell, of which traces are present, is 

 very thin. The first species is from the Trichinopoly, the second from the Ootatoor group. 



POROMYA. 



07-09. — I am acquainted for the present only with the three Indian species, P. globii. 

 losa, lata, and superba (see p. 47, &c.) . The two former were, without any apparent reason, transferred by 

 D'Orbiguy to Lyonsia. Forbes also considered the Corb. aquivalvis of GoMdiss as a Poronu/a, 

 but according to the hinge it does not belong to this genus, though the surface is partially provided 

 with minute grooves. I shall describe it under Pholadomya, and state the necessary reason for this 

 alteration subsequently. 



Lutraria nuculaformh, Schafh., (Bayern's Leth. Geog., p. 175,) I would be inclined to 

 consider as identical with our P. globulosa, at least the general form of both is the same. The form, 

 figured by SchafhcLutl, loc. eit., (pi. 41, fig. 2,) as Corbula impressa (1863, uon idem, Eichwald 

 Leth. Ross., liv. xi, 1807, p. 741,) is probably also a Toromya. 



I am not certain whether Zittel's Tanop.frequensixovix'CciQ Gosau (Denksch. Akad., Wien, 1865, 

 xxiv, pt. ii, p. Ill, pi. 1, fig. 5,) does not also belong to the present genus. The form and the general 

 character of the shell are almost identical with those of our P. lata, but the hinge is veiy similar 

 to that of a P«»o^«a, or rather to that of P/««ro»2^a y it has, however, like Poromya, one tooth in 

 each valve and posterior to it a groove, in which, in the last genus, the cartilage is situated. 

 Whether that was the case with the species in question, Zittel's figure does not show clearly, for 

 the tooth in the left valve is placed too much anteriorly, almost more so than that of the right 

 valve, behind which it ought to fit when the valves are closed. The most important distinction 

 to be observed in ZitteTs figure, is the isolation of each of the teeth along the lower margin, 

 while in Poromya the inner hinge area is thick, and the teeth and pits generally appear on it as 

 projections and grooves. In specimens of our collection the hinge-teeth could unfortunately not be 

 made visible, and the shell surface is also not well preserved. — I expect several of D'Orbigny's 

 Panojjfca vnW be shown to belong to Poromya; in some, like P. ??;('e(5'?(/i-rt:/f«, the author describes 

 the granulation of the surface, similar to that of Poromya, but quite distinct from that of Panoj)eea. 



I have already mentioned Corbula oblusa, which Bosquet considered to be a Poromya. Ceromya 

 recens, Pholadomya aptiensis, and fallax described by Coquand in his Monograph of the Fossils of 

 the fitage Aptien of Spain are more likely Poromya than Ceromyre. I am also by no means certain 

 whether such species as Pholodonya Sanctcc-crucis, or PJi. Falangiensis of Pictet and Campiche, 

 ought not to be more correctly referred to Poromya than to Pholadomya. 



Judging from external appearance and the imperfectly known hinge, I suppose Corbula glgantea. 

 Sow., (Min. Conch., vol. iii, p. 13, pi. 209, figs. 5-7,) is also a Poromya. It very much resembles 

 our Por. siiperba, diflTcring from it by the anteriorly extended portion of the shell. The species 

 has been placed by Morris in the genus Thetis, that author having considered Forbes' Poromya 

 as identical with Thetis, which opinion is, as I have already stated, untenable. Pictet and 

 Campiche (Pal. Suisse, 4th Ser., 3°"= pt., p. 210,) are of opinion that the species probably 

 belongs to a new genus; it is said to possess the same deep sinus, as Thetis has, but Sowerby does 

 not s.iy anything on this point; unless, therefore, Pictet and Campiche have examined fresh 

 specimens, the question would still remain unsettled. 



These arc only a few of the most prominent instances indicating the occurrence of Poromya in a 

 fossil state. I could add a much greater number of suggestions regarding the generic determination 

 of the cretaceous species, but it would bo hardly fair to go into these details without the examination 



