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911 



TERTIARY FAUNA OF FLORIDA 



upon and nearly destroyed the posterior arm of the cardinals; but in the two 

 Eocene species upon which this genus was founded the pit does not descend 

 more than half way from the dorsal border to the ventral margin of the hinge- 

 plate. The pallial sinus is small but well marked. The type is M. csqtiorea 

 Conrad, Tert. Fos., p. 42, 1833 (= Mactra Grayi Lea). M. rectilinearis Con- 

 rad is a somewhat larger species from the same horizon. The intermediate 

 state in which the hinge is found in this genus is good evidence that in 

 America, at least, this family is not lil-cely to be found in earlier than Eocene 

 rocks. 



Genus AI'ACTODBA Call. 

 Papliia Lam., iSoi {fx pa)-ic), not Bolteii, 1798; Erycina Sby., 1S22, not Lam., 1S04; 



Mesodesina sp. Desh., 1835 i E>yx Swainson, MalacoL, p. 370, 1840, not Daudin 



nor Stephens, 1832. 

 Atactodea DalL, Proc. Mai. Soc. Lond., i., p. 213, 1895. 

 Type Papliia glabrata Lam. ; Indo-Pacific region. 



Shell subtrigonal, strong, concentrically sculptured or smooth ; pallial 

 line with a short, well-marked sinus; hinge strong, ligament submarginal, 

 obsolete ; cartilage narrow, strong ; dorsal areas not differentiated. 



The group is exclusively old world and especially tropical, extending 

 from the Red Sea to Japan and south to Mauritius. The species are few and 

 ■ mostly very similar in appearance ; the soft parts are unknown. 



Geuus MESODESMA . Dcsliayes. 

 Mesodesina Desh., 1830, Enc. Meth., Vers, ii., p. 442. 

 Type M. donaciicin Lam. (+ M. chilcnse Orb.) ; Chile. 



Subgenus MESODESMA s. s. 



Shell donaciform or subtrigonal, inequilateral, solid, with a thick epi- 

 dermis, smooth or concentrically striated, posterior end subtruncated, shorter; 

 dorsal areas not differentiated ; hinge strong, resiliary pit large, deep, with 

 raised margins ; ligament short, chiefly internal ; lateral teeth transversely 

 sulcate, strong, the anterior elongated ; pallial sinus well marked. 



Ceronia Gray, 1853, is a synonyme. The .species are found in temperate 

 waters of both shores of -South America, New Zealand, and the northeastern 

 shore of North America. M. arctatuni Conrad and M. deauratuni Turton 

 are known from the Pleistocene of eastern North America, north of Cape 

 Cod, and AI. Bishopi^Nhite (Powell, Rep. Geol. Uinta Mts., p. 128, 1876) has 

 been described from the western brackish-water Tertiary, but the exact locality 



