MARYLAND .GEOLOGICAL SURVEY 633 



Outside Distribution. Ripley Formation. Exogyra costata zone, 

 Eufaula, Alabama ; Union and Tippah counties, Mississippi. Extreme 

 top of zone, Chattahoochee River, Alabama. 



Family ANATINIDAE 



Genus PER1PLOMYA Conrad 

 [Am. Jour. Conch., July, 1870, vol. vi, p. 76] 



= Leptomya Conrad, 1867. Not Leptomya A. Adams, 1864. 



= Plicomya Stoliczka, November, 1870. 



Type. Periploma appUcata Conrad. 



" Elongated, inequivalve, thin, perlaceous, gaping anteriorly ; hinge 

 with a projecting spoon-shaped cartilage process, narrowing gradually 

 towards the inferior end, which is acutely rounded; this process joins an 

 oblique callosity which extends to the cardinal margin ; an obsolete rib and 

 fissure run obliquely from the anterior side of the apex. This genus, 

 which is allied to Anatina, differs from it in having a tapering cartilage 

 process attached to a rib or support which joins the hinge margin ante- 

 riorly; and in having the fissure anterior to the apex, and running 

 obliquely towards the anterior extremity of the ventral margin. This 

 genus is known in this country only by one species, which is found in the 

 Eipley group of the Cretaceous era. Judging from external characters 

 and outline of the shells, I should suppose that d'Orbigny's Periploma robi- 

 naldina, P. necomiensis and P. simplex are species of Leptimya, which 

 genus probably became extinct with the Cretaceous fauna. The gape of 

 the anterior is moderate, and valves but slightly reflexed, in which respects 

 it differs essentially from Anatina" 1 Conrad, 1867. 



FEUIPLOMYA ELLIPTICA Gabb 



Anatina elliptica Gabb, 1862, Proc. Acad. Nat. Sci., Phila. for 1861, p. 324. 

 Anatina elliptica Meek, 1864, Check List Inv. Fossils, N. A., Cret. and Jur., 

 p. 15. 



Etymology: (?)A name suggested by the resemblance of the form to 

 Periploma and Mya. 



1 Conrad, 1867, Am. Jour. Conch., vol. iii, p. 15. 



