42 . PALEONTOLOGY OF NEW JERSEY. 



Arca (Striarca) centenaria. 

 Plate VI, figs. 5-7. 



Area centenaria Say : Jour. Acad. Nat. Sci., PhiL, vol. 4, 1st series, p. 138, PL x, 

 fig. 2; (Jourad, Foss. Shells Tert. Form., p. 16, PI. i, fig. 4; Miocene Foss., 2>- 

 55, PI. 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{Saj) Conrad: Cat. Miocene Foss., Phila. Acad. Nat. Sci., 1862. p. 

 580; PliiL, Meek, Check List Miocene Fossils, p. 6. 



Mr. Say's original description and diag-nosis of this species is as fol- 

 lows: " Shell transversely-oval, subrhomboidal, obtusely contracted at base, 

 with numerous alternate longitudinal striae. * * * Striae from 100 to 

 180 and more in number; disappearing on the hinge margin; with hardly 

 obvious transverse minute wrinkles, and larger, remote, irregvilar ones of 

 increment; heaks but little prominent, not remote; base widely but not 

 deeply contracted, nearly parallel with the hinge margin; anterior ixnd 2>os- 

 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 

 ca\dty 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 striae on the New Jersey 

 shells are most beautifully creuulated, even on very small specimens, where 

 it requires a lens to see them; and on the larger ones proportionally dis- 

 tinct. The striae are seen to constantly increase in size with the increased 

 growth of the shell, consequently their niunber will be vai'iable 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 mai-giu, but 

 • merely a few points dependent on the surface striae, but which are oblit- 



