482 
Older— PHOLADACEA. 
I’amily— GASTROCHiENID^. 
Genus— GASTBOCH^NA, Spengler, 1783. 
Oastrochmia, Spengler (Lamarck partim), Saral. Kongl. Banks. Vid. Selsk. Skr., ii., p. 174. 
Chcena, Pbillipason in Retzius, Dissertatio Hist. Nat., 1788, p. 19. 
Gasteochjjna ArsTEALis, sp. non., P], 31, figs. 6-8. 
Sp. Char. Valves unlcnown. Tube tapering but little in tlie fragment preserved, 
secHon nearly round. Surface covered vsdth very fine anastomosing lines, wbicb are 
tbe broken off, or rubbed down edges of a series of sbelly frills, forming by their 
anastomosis transversely elongated spaces. 
Ohs. This object for a long time defied determination, but I believe the shell 
structure of tlie living Qastroohaina grandis, Desh., will explain its nature. 
In the tube of the recent species the structure of the outer layer is vesicular, 
arising from the mechanical union of frilled surfaces with particles of sand. If this 
vesicular structure be broken, or worn-down, a series of anastomosing frills or ridges 
are formed, enclosing vesicles or chambers, usually transversely elongated. Supposing 
these to be still further denuded, the resulting structure would be a series of 
anastomosing lines on the fossil, instead of frills. Such is, I believe, the origin of 
those seen on the specimen now under description. 
A species has been described from the Cretaceous rocks of India, but it is 
quite different from the above. 
Loc. Maraiioa River, half a mile above Mitchell River Station (It. L. JacTc) . 
PELECYPOD^ INCEET^ SEDIS. 
Ohs. Under this heading are placed a few bivalves which it has been found 
impossible to relegate to their proper genera. They are figured, or refigured, as the 
case may be, in the hope that attention may be called to them, and additional 
examples obtained for further elucidation. 
Pn. 21, Pig. 15. — A somewhat rectangular valve, with the umbo quite at the 
anterior end, a nearly straight cardinal margin, and but little convex surface, which is 
marked with a few concentric laminje. The posterior margin appears to be slightly 
emarginate. Under it is another individual, which may be the opposite valve of the 
same species, bearing six rib-like cost*, and shorter intermediate ones. 
Loc. Aramac (B. L. JacJc). 
Pl. 21, Fro. 16. — A nearly flat meleagriuiform valve without any anterior ears, 
an inconspicuous umbo, short cardinal margin, slightly emarginate posterior margin, 
and indistinct concentric lines. This bears a striking resemblance to left valves of 
Whitfield’s genus Meleagrinella,* and which it may even represent, but I have not seen 
any corresponding right valves possessing the peculiarities of that genus. It is like 
AT. ahrupta, Conrad, sp.f, and to some extent AT. curia. Hall, sp.J Some resemblance is 
also borne by our shell to the Indian Cretaceous species Pseudomonotis inops, Stoliczka. 
Loc. Aramac (i2. L. Jack). 
Pl. 21, Fig. 14. — A bivalve of a somewhat similar type to the above, but too 
indistinct and imperfect to have tuuch stress laid upon it. The umbo is much more 
median, and the ornament is concentric. 
Loc. Coreena Woolshed {B. L. Jack). 
* Mon. U. S. Geol. Survey (Powell’s), 1885, ix., p. 71. 
+ Whitfield, loo. cit, t. 14, f. 11. 
t U. S. Geol. Survey Rocky Mt. Region (Powell’s), Whitfield’s Pal. Black Hills of Dakota, p. 354, 
t. 3, f. 20. 
