MIOCENE MOLLUSCA AND CRUSTACEA. 35 



Genus PLICATULA Lamarck. 



Plicatula densata. 



PI. v, figs. 3-8. 



Plicatula densata Conrad: Proc. Acad. Nat. Sci. Phil., vol. I, p. 311; Miocene Fossils, 

 p. 75, pi. 43, fig. 6; Cat. Miocene Fose» Atlantic Slope, Proc. A. N. Sciences, p. 

 582; Meek, Check List, Mioc. Foss., p. 4; Heilprin, Cont. Tert. Geol. and Pale- 

 ont. U. S., p. 8. 



" Ovate, thick* profoundly and irregularly plicated; inferior valve ven- 

 tricose; ribs acute, with arched spiniform scales; cardinal teetli large, curved, 

 laterally striated, crenulated on the margins; larger cardinal tooth in each 

 valve slightly bifid, broad; muscular impression prominent. * * * The 

 valves have about ten folds, and the lower valve closely resembles a variety 

 of Ostrea Virginia/no,." (Conrad.) 



The form of this shell is extremely diversified, as much so as any 

 species of the genus I have ever examined. The lower valve has usually 

 been fixed to some foreign substance, sometimes by the smallest portion of 

 the apex and at others by the entire under surface of the valve, showing 

 plications only $Jong the edge, and all degrees between these extremes are 

 readily found. 15he upper valve is not uncommonly entirely destitute of 

 plications and strongly lamellose, resembling the valve of an oyster; this 

 more commonly where the lower valve has been attached over almost its 

 entire surface. In others the upper valve is as strongly plicated nearly to 

 the beak, as is the lower, and with the plications fully as angular, though 

 generally they are rounded, while those of the lower are sharply angular. 

 In number of plications they vary as much accordingly as the shells do in 

 form, those of the lower valve often being as many as twenty, counting 

 those on the margin, and others having as few as seven or eight. The 

 surface of the valves is strongly rugose-lamellose, often marked by strong 

 points. The substance of the shell is quite thick and dense, and the mus- 

 cular imprints usually elevated. The shells are almost as diverse in outline as 

 numerous in individuals. Teeth but slightly divergent and strongly inter- 

 locking, so as to separate with difficulty or by fracture only. 



Localities: I have seen specimens of this species from Shiloh, Jericho, 



