e 
MUSEUM OF COMPARATIVE ZOOLOGY. 205 
Pleurotomella atypha, sp. nov. 
Plate I, Fig. 3. 
Two dead specimens, Station 325, in 647 fathoms, and one living specimen, 
Station 326, in 464 fathoms, off Cape Fear, N. C. 
Shell rather large, solid, somewhat translucent, bluish white, with a com- 
paratively smooth surface and little lustre. Spire unusually high, consisting 
of nine angularly shouldered whorls below the small, very acute, chestnut- 
brown nucleus. Aperture short, broad. Posterior sinus as broad as the sub- 
sutural band, rather shallow. Outer lip considerably inflated, curving grad- 
ually toward the columella without forming a decided canal. Columella 
nearly straight, curved slightly anteriorly, with a narrow, closely adhering 
strip of enamel. Suture distinct, undulating, slightly channelled. Subsutural 
band rather broad, oblique, somewhat concave, ornamented on the upper 
whorls with fine, distinct, curved riblets and lines of growth, the latter alone 
being visible on the two lower whorls. Just above the periphery, at 
the edge of the subsutural band, very narrow, sharp, slightly raised, oblique 
ribs, separated by very wide, slightly concave spaces, cross the whorls to the 
suture, and on the body whorl disappear just below the sutural line of the 
aperture. These ribs are most conspicuous at the shoulder, and vary consid- 
erably in different specimens, changing from the above narrow, sharp ones, 
with wide interspaces, to others broad and rounded, with narrower interspaces, 
the number on the body whorl varying from twelve to fifteen. The entire 
surface, except the nucleus and subsutural band, is cut by fine, shallow grooves 
separated by flattened spaces of unequal width ; these are deeper and coarser, 
or broader, on the lower part of the body whorl and canal, causing the spaces 
between them to appear as raised rounded threads. Nucleus long, very slen- 
der, consisting of four and a half finely reticulated light chestnut-brown whorls. 
The apical whorl is imperfect, but must have been very minute, judging from 
the size of the succeeding one. 
Length of the largest specimen, destitute of the nucleus and one or two upper 
whorls, 30 mm.; greatest breadth, 12 mm.; length of aperture, 13.5 mm. ; its 
greatest breadth, 4 mm. A smaller specimen with a nearly perfect nucleus 
is 23.5 mm. long; about 8.5 mm. broad ; width of the last nuclear whorl, 
0.5 mm. 
This species resembles in general appearance the elongated form of Plewro- 
tomella Agassizit V. & S., but is quite different in detail. The most apparent 
distinguishing characters are its high, finely pointed spire and nearly smooth 
surface. 
It is perhaps closely related to the much smaller Plewrotomella filifera Dall 
(this Bulletin, IX. p. 56, 1881; XVIII. p. 123, pl. 12, fig. 9, 1889). The 
figure quoted was evidently made from a specimen with an imperfect nucleus, 
as it shows but seven whorls. 
