2:>0 UNITED STATES GEOLOGICAL SURVEY OF TOE TERRITORIES. 



Hanley nine years later, from much better specimens than that upon which 

 Professor Forbes originally founded the genus. I have not seen his firsl 

 description, published in 1844 (Report on the Moll. ^Eg. Sea, 143), but it 

 seems that he had but an imperfect specimen, as the diagnosis published 

 by him and Hanley (Hist. Brit. Moll., I. 203), in 1853, is said to have been 

 made out from a much more satisfactory specimen. Their diagnosis, in the 

 latter of the works quoted above, gives the hinge-characters as follows: 

 "a minute cardinal ossicle or erect tooth in one valve, lodged in a pit or 

 rather depression in the other; no lateral teeth." The ligament they here 

 describe as being " external,'' and the pallial line as being "very slightly 

 sinuated." 



It is evident that Professor Forbes was unacquainted with the hinge- 

 characters of the East-Indian Cretaceous shells, already alluded to as having 

 been by him referred to Poronnja, in 1N44 (Trans. Geol. Soc. London, '2d 

 ser., VII, 140) ; because he does not illustrate the hinge in any of his figures, 

 or mention it in his description of any of the species: while in a generic 

 diagnosis given there, he describes the hinge (evidently from the true 

 Poromya and not from the Cretaceous species then before him) as having 

 "in the right valve a strong cardinal tooth," and in the left, the "cardinal 

 tooth obsolete;'' characters which, it will be seen, are quite different from 

 what the Indian Cretaceous species, then before him, are now known to 

 present. 



Nine years later (Appendix to Hist. Brit. Moll., IV, 250), Professors 

 Forbes and Hanley give a more detailed description of Poromya from per- 

 fect recent specimens, in which they describe the hinge as having under the 

 beak of the right valve "a strong and bluntly-cloven tooth, which, rising from 

 the lower edge, curves with some slight obliquity upward," and farther add, 

 that " a short and very small triangular cartilage-pit occupies the upper portion 

 of the area behind it." The hinge of the left valve they here describe as 

 having "the hinder half of the plate slightly hollowed out, excepting at the 

 lower edsre, as a subtrigonal shallow depression, that is barely divided in 

 front below by an obscure thin ridge, from the tiny but deep triangular exca- 

 vation (which receives the opposite tooth): the remaining level, or slightly- 

 raised anterior surface, which projects, with a somewhat bifid extremity above 

 the latter, into the large triangle, suggests the idea of a complicated 

 dentition.'' 



