OP SOUTHEEX INDIA. (50 



appears to be the small Anat. gracilis from Australia, though this does not show 

 the character of the siphonal end so well as the fossil forms do. 



30. Plectomija, Loriol, 18G8, (Monog. Pal. Geol. etage Portlandien de 

 I'Yonne, p 89 : ? = Platymya, Agassiz). Shell ovately elongated, equivalve, beaks 

 sub-central, a strong oblique rib posterior to them; hinge edentulous; ligament 

 external. This genus has been based upon a well known Jurassic fossil, the Tellina 

 riigosa of Eomer. Its general form is that of an Anatina, and if there be no trace 

 of an internal cartilage-pit, nor of a fissure dividing the beaks, the genus may be 

 retained. But I rather doubt this ; we need only to look upon such species as Anat. 

 Agassi zi, d'Orb., to find a reason for it. However, even should Loriol' s definitions 

 prove to be quite correct, it appears to me that Agassiz' Flatymya has priority, 

 for judging from external appearance Flatymya rostrata, Ag. (Etud. crit., pi. 10, 

 figs. 11-12,) exhibits all the above noted characters of a Flectonuja. 



31. CyatJiodonta, Con., 1849, (Proc. Acad., &c., Phil., vol. iv, p. 155). 

 Shell like Anatina in form ; " hinge with a broad, not very projecting fosset, which 

 is carinated near the margin ; muscular impressions rounded, indistinct ; pallial 

 impression with a large rounded sinus." No mention is made of any kind of the; 

 fissure at the beaks. H. and A. Adams consider the genus identical with Anatina, 

 but Conrad in his last catalogue of the family keeps it distinct, referring to it four 

 different species. 



32. Plicomya, Stoliczka, 1870, {Leptomya* Conrad, 1867, Am. Journ. 

 Conch., Ill, p. 15). Shell oblong, perlaceous, gaping anteriorly; hinge with a 

 spoon-shaped cartilage process, joining an oblique callosity, which extends to the 

 cardinal margin ; an obsolete rib and fissure run obliquely from the anterior side of 

 the beak. The genus is evidently closely allied to Anatina, from which it chiefly 

 differs by the rib and fissure anterior to the beak ; it is based upon a cretaceous 

 species from N. America. Conrad suggests that d'Orbigny's Peripl. Bobinaldina 

 and two others probably also belong to his Leptomya, but I think that they are more 

 probably species of Corimya. 



33. Anatimya, Conrad, 18G0, (Jour. Acad. Nat. Sc, Phil., 2nd Ser., iv, p. 276). 

 Shell oblong like an Anatina, anterior side with concentric sulci, posterior with 

 radiating ribs. This form appears to be peculiar to cretaceous deposits. There are 

 as yet only a few American species known. 



34. Anthracoinya, Salter, 1861, (Mem. Geol. Surv. of Great Britain, "Iron 

 Ores," pt. iii, p. 229). Shell thin, nearly equivalve, left valve a little smaller than 

 the right one, dilated posteriorly, but closed anteriorly, rounded ; posterior hinge line 

 vni]x a narrow anterior ridge ( ? like in Gresslya) ; ligament external. This is 

 based upon Anth. Aclamsi, Salt., and a few other carboniferous fossils. The char- 

 acters somewhat recall Conchocele, Gabb, which, however, may be better placed 

 in the Lvcisidm. Salter states that Anthracomya was either marine or brackish, 

 and that it occurs •witli Anthracosia (JInionidjeJ in the same beds. 



* Non idem A. Adams, 1864 (Scrodwulariid^). 



