240 PALEOZOIC PALEONTOLOGY. : - 
Remarks.—The pedicle valve of this abundant species of the lower 
Decker Ferry beds is most commonly preserved, brachial valves being 
comparatively uncommon. ‘The species may usually be recognized by 
its inconspicuous plications, though in some individuals, particularly 
the younger ones, they are wholly obsolete. Most of the specimens are 
exfoliated so that the fine, concentric markings of the surface are 
usually obliterated, but they may be detected upon occasional speci- 
mens. 
RHYNCHOSPIRA FORMOSA Hall. 
Plate XXI., Kigs. 30-34. 
1859. Trematospira formosa Hall, Pal. N. Y., vol. IL., p. 215, pl. 36, 
figs. 2 a-t. 
1859. Rhynchospira formosa Hall, Pal. N. Y., vol. IL, p. 485, pl. 
95 A, figs. 7-11. 
1893. BRhynchospira formosa H. & C., Pal. N.Y., vol. Vii pias 
p. 109, pl. 50, figs. 21-25. 
Description.—Shell ovoid in outline, usually a little longer than 
wide, valves subequally convex, rostrate posteriorly, rounded in 
front, usually with a slight emargination in the middle. Pedicle 
valve with a prominent, incurved beak and with a narrow, flattened 
or depressed area along the mesial line. Brachial valve usually most. 
prominent posteriorly, the beak incurved under that of the opposite 
valve, the mesial line usually flattened in a manner similar to the 
pedicle valve but less conspicuously. Surface of each valve marked. 
by sixteen or eighteen rounded or subangular radiating plications, 
those on the lateral slopes being simple and continuing to the beak, 
while those in the mesial depressions are usually a little finer and often 
do not continue to the beak. 
The dimensions of a somewhat crushed specimen are: length, 10 
mm.; width, 9.5 mm.; thickness, 5 mm. A more gibbous specimen 
with a similar length and width has a thickness of 7 mm. 
Remarks.—The specimens of this little shell from the coralline layer 
of the Decker Ferry formation do not differ essentially from those in 
the Helderbergian faunas, except that the shell is more uniformly 
strongly plicated, not showing so great a variation in this respect as 
