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QI I 



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. (cqnorea 

 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 likely to be found in earlier than Eocene 

 rocks. 



Genus ATACTODEA Dall. 

 Papliia Lam., 1801 (,-x pur/,-), not Holten, 1798; I'lrycina Shy., 1822, not Lam., 1804; 



,M,->tifsniii sp. Desh., 1835 '> /''J'- 1 " Swaiiison, Malacol., p. 370, 1840, not Dauclin 



in ir Stephens, 1832. 



Alnclnilt'ii Dall., I "roc. Mai. Sue. Loud., i., p. 213, 1895. 

 Type 1'iT/iliiit gliil/mlii Lam. ; huln-I'acilic region. 



Shell subtngonal, 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. 



Genus MBSODESMA. Ix-sluiycs. 

 M,-Mi,l,-Miia iK-bh., 1830, Knc. Meth., Vers, ii., p. 442. 

 T\ pe .!/. tlntiitciuni Lam. (- .17. chilcnsf Orb.) ; Chile. 



Subgenus MESODESMA s. s. 



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

 dermis, smooth or concentrically striated, posterior end siibtruncatcci, 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. 



Ceroiiia 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. J/ arctatmii Conrad and M. tlantratitiii Turton 

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

 Cod, and M. His/topi White (Powell, Rep. Geol. Uinta Mts., p. 128, 1876) has 

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



