42 PALEONTOLOGY OF NEW JERSEY. 
ARCA (STRIARCA) CENTENARIA. 
Plate vi, figs. 5-7. 
Arca centenaria Say: Jour. Acad. Nat. Sci., Phil., vol. 4, 1st series, p. 138, Pl. x, 
fig. 2; Conrad, Foss. Shells Tert. Form., p. 16, Pl. 1, fig. 4; Miocene Foss., p. 
55, Pl. 29, Fig. 4; Tuomey and Holmes, Plioc. Foss. So. Car., p. 37, Pl. Xv, figs. 
11 and 12: Emmons’s Geol. N. Car., pp. 284, 205. 
Striarca centenaria(Say) Conrad: Cat. Miocene Foss., Phila. Acad, Nat. Sci., 1862. p. 
580; Phil., Meek, Check List Miocene Fossils, p. 6. 
Mr. Say’s original description and diagnosis of this species is as fol- 
lows: “Shell transversely-oval, subrhomboidal, obtusely contracted at base, 
with numerous alternate longitudinal strie. * * * Striz from 100 to 
180 and more in number; disappearing on the hinge margin; with hardly 
obvious transverse minute wrinkles, and larger, remote, irregular ones of 
increment; beaks but little prominent, not remote; base widely but not 
deeply contracted, nearly parallel with the hmge margin; anterior and pos- 
terior margins obtusely rounded; series of teeth rectilinear, uninterrupted, 
decurved at the tips; space between the beaks with numerous grooves 
proceeding from the teeth; inner margins not very distinctly crenated; mus- 
cular impressions elevated, and forming a broad line each side, from the 
cavity of the beak to the margin.” 
All the specimens of this shell which I have seen from the New Jersey 
marls are greatly dwarfed in size, specimens of an inch and a quarter 
being of very large size, while most of them are below three-fourths of an 
inch in length. With this exception they are pretty close representatives 
of the shells from Maryland and Virginia. The striz on the New Jersey 
shells are most beautifully crenulated, even on very small specimens, where 
it requires a lens to see them; and on the larger ones proportionally dis- 
tinct. The striz are seen to constantly increase in size with the increased 
growth of the shell, consequently their number will be variable according 
to the size of the specimens. The hinge line is strongly striated vertically, 
but few show the usual diverging ligamental grooves, seen on other Areas. 
None of those examined show proper crenulations of the margin, but 
‘merely a few points dependent on the surface striz, but which are oblit- 
