W. B. Dwight — Wappinger Valley Limestone. 453 
mens are so exceedingly brittle as to render them difficult of 
extraction without injury, and as to require great caution in 
the handling after they are secured. Of the ventral valve, I 
have found but four or five sufficiently perfect to show the 
peduncular groove; of the epi valve I have obtained twice 
satisfactory exhibition of the general surface of both si 
the same individual valve ; for the action of acid in separating 
the imbedded side from the rock is apt to flake it off injun- 
ously. The margins of the specimens are almost invariably in: 
a broken state. 
The shell has been above described as lamellose. I se not 
the adjoining parts. In most cases, however, nothing but the 
simple concentric lines of the ieee are visible. 
EXPLANATION OF PLATE. 
Figures 1, 2 and 3.—Apical portions of the lower ceniral) ngs of three differ- 
ent individuals, actual size, showing the peduncular groove o. 3 shows a tend- 
sr form 
ency to ide ac spre rm. 
riety fe specimen figure 1, enlarged 24 diameters, to show the 
igure 
reo of the 3 cig aes ion roe the foramen (at 7) and the strongly marked 
centric 
aes: re 4,— wer valve, actu ape estate a broadly flattened 
eure ther lo tual 
margin, to the diminution of the height of the 
Figure 5.—The largest pee valve yet pe geval a regular cone; the mar- 
ginst od a ey aed ; (actu 
Fi gment af + “apper (dorsal) valve, actual size, showing the apex 
gure 
and considorale oneatie of t ety between the apex and anterior margin. 
Fi —A nearly perfect rae y flat specimen of the upper valve showing 
the apex x eligi or Ae and about + ‘Manet r from the nearest margin. 
Figure 7 show tric rid 
‘ e, nified two dia concentric ridges. 
Figure 8.—A cross section through a pipet of the ce valve, extending from 
t a, a short di towa e rior margin, mag nine times, 
showing the laminations of the shell and the abies of the ridges. 
Figure Sig 3 section of upper valve, near posterior margin, parallel to the 
shorter Sap 
igure ne 11.—Interiors of upper valves - two individuals, are size, 
sonletwe. teats the pallial ap ape and one pair of muscular impre with 
Some indications of a second pair near the 5 paaiclor margin (lower pert t of the 
Sines 
Figure 11 a,.—An enlargement, two diameters, of specimen figure 11 
Figure 12.—An ideal profile of the two valves united and in position. 
