228 BULLETIN OF THE 
acute, and turned directly inward, with a long, narrow ligamental furrow on 
the posterior side, which on the inner surface extends far inward in a transverse 
direction, as a narrow dark brown groove with a raised margin ‘on each side. 
The antero-dorsal margin is a little convex, and broadly arched anteriorly, with 
a wave-like inbending of the margin below corresponding to a broad shallow 
depression extending from the umbos to the edge. The ventral margin is very 
broadly and evenly rounded, separated from the posterior region by a distinct, 
wave-like incurvature, corresponding to a double furrow running from the pos- 
terior side of the beak to the margin. The posterior region is a little prolonged 
and subtruncate at the end. The postero-dorsal margin slopes from the beak 
and is nearly straight, joining the posterior margin in a rounded angle. 
“The cartilarge pit is moderately large, thick and strong, spoon-shaped or 
ovate, and curved obliquely backward, with the cartilage area in the form of 
a wedge-shaped depression; the plate is supported by a broad, thin rib, which 
runs from its inner surface inward and somewhat backward for a considerable 
distance; another much smaller rib runs from its posterior surface backward 
to the margin, leaving a triangular cavity between it and the principal rib. 
The pallial sinus is moderately large and deep, extending directly backward. 
from the posterior tip, tapering and terminating in a bluntly rounded end, 
The inner surface, somewhat pearly and slightly concentrically waved, is also 
marked with rather indistinct radiating lines. The external surface is covered 
with rather conspicuous and narrow, unequal, concentric grooves and lines of 
growth ; anteriorly there is a broad shallow transverse undulation, while 
posteriorly a narrow shallow depression, defined by two distinct furrows, 
curves from the beak to the posterior ventral margin ; farther back a small, 
distinetly raised ridge extends from the posterior side of the beak to the poste- 
rior end; the area between this and the dorsal margin is covered by numerous 
fine radiating lines, not distinctly visible without a lens. The epidermis 
is thin and closely adherent, with irregular, raised, fibrous, concentric lines in 
some parts, especially on the posterior area, 
“Length, 40 mm.; height from ventral margin to beak, 31 mm. ; breadth, 
16 mm. ; length from beak to anterior end, 23 min.; to posterior end, 15 mm.; 
length of cartilage plate, 3 mm.; length of internal rib, 9 mm. ; its greatest 
breadth, 2 mm. ; length of pallial sinus, 18 mm. ; its breadth in middle, 8 mm.” 
Periploma fragilis (Torren). 
Anatina papyratia Totten, Am. Journ. Sci., XXVIII. p. 847, pl. fig. 1, a, b, c, d, 1835. 
Periploma fragilis Conrad, Am. Journ. Conch., II. p. 106, 1866. 
Anatina papyracea Gould, Invert. Mass., Binney’s ed., p. 66, fig. 882, 1870. 
Periploma papyracea Verrill, Invert. Anim. Vineyard Sd., p. 379, pl. 27, fig. 197, 
1874; Trans. Conn. Acad., VI. p. 277, 1884. 
Periploma fragilis Dall, this Bulletin, XII. p. 306, 1886; Bulletin U. S. Nat. Mus., 
No. 37, p. 64, pl. 59, fig. 7, 1889. 
Nine living specimens and two valves, Station 344, south of Martha’s Vine- 
yard, in 129 fathoms. 
