MIOCENE MOLLUSCA AND CRUSTACEA. ap 
Genus PLICATULA Lamarck. 
PLICATULA DENSATA. 
Pl. v, figs. 3-S. 
Plicatula densata Conrad: Proc. Acad. Nat. Sei. Phil., vol. 1, p. 311; Miocene Fossils, 
p. 75, pl. 43, fig. 6; Cat. Miocene Foss. 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 teeth 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 Virginiana.” (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 along the edge, and all degrees between these extremes are 
readily found. The 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 
D3) 
Localities: 1 have seen specimens of this species from Shiloh, Jericho, 
so as to separate with difficulty or by fracture only. 
