ILL USTRA TIONS F A MERICA N SHELLS— DA LL. 523 
subsequent whorls regularly increasing; otherwise as in Tritonofu- 
sus s. s. 
Subgenus Plicifusus 0:111, 1902. Tj'pe, Fmus hroyeri Moller. 
Shell solid, usually with developed axial ribs and feebler spiral 
sculpture; the aperture expanded and with a wide insinuation behind 
on the outer lip; canal usually short and wide, nearly straight; other- 
wise as in Tritonofu.ws s. s. 
Subgenus Ancistrolepis Dall/ Type, Ckrysodomvs eitcosmius Dall, 
Bering Sea. 
Shell bucciniform, with a short twisted canal and the operculum 
claw-shaped, concave, with apical nucleus; penis on a stout stalk with 
the distal extremity pediform, enlarged, without a terminal papilla; 
dentition as in C%rysodomus^ but the radula is degenerate and dispro- 
portionatel}^ small. The periostracum is conspicuous and villous. 
Subgenus Mohnia Friele, 1878. Type, Fusus mohnii Friele. 
Shell as in Siphonorhis or Plicifusus^ but the whole nepionic shell 
smooth (it is sculptured up to the larval whorls in the other species); 
operculum coiled, pauci-spiral; radula, with one cusp on the rhachidian 
and two on each lateral tooth; ovicapsules solitary, as in Tritonofusus. 
Genus Volutopsius Morch. Type, Stromhus iim^vegicus Gmelin. 
Shell large, solid, with a short spire, ample last whorl and short, 
wide canal, the ovate operculum not closing the aperture in most of 
the species; the nucleus small, swollen, globose; the ovicapsules large, 
solitary, hemispherical, attached by the whole of the broad side, con- 
taining several embrj^os. Dentition as in Chrysodcmius, hut irregular. 
In these forms the shape of the shell does not appear to be corre- 
lated with sex. The sculpture is variable, often rude, sometimes with 
broad obscure axial ribs, but usually almost entirely spiral, varj^ing 
from very fine to coarse in the different species. They are confined 
to the colder waters of the Northern Hemisphere and are especially 
numerous in the region of Bering Sea. 
Subgenus Pyrolofusus (Beck) Morch. Type, Fxisus deformis Gra3^ 
Shell large, thin, usually sinistral; spirally striated, axially obscurely 
folded, with a ver\^ large swollen nucleus; operculum much smaller 
than the aperture, subquadrate; canal short, wide; spire short, last 
whorl much the largest; dentition chr3"sodomoid, but rather irregular, 
the cusps of the rhachidian tooth small, some of them sometimes obso- 
lete; laterals with the terminal cusps large, the central cusp often 
absent or obsolete; ovicapsules solitar}', large, and hemispherical, 
attached as in Vohitopsius, containing few embryos. 
The Alaskan species is almost alone among the Chrysodomoid forms 
in exhibiting bright colors (salmon, orange, or rose-pink) in the 
enamel of the aperture. A pliocene form from Arctic Alaska is dex- 
tral and has a few very strong axial ribs. 
iProc. U. S. Nat. Mus., XVll, 1895, p. 709. ' 
