GASTEROPODA. 189 
Trocuus (Monoponra) aTropuRPuREuS (Gould). 
Testa parva, depressa, ovato-conica, atropurpurea, liris granulosis 
ubique cincta: spira anfractibus quinque ad sex, ultimo subangulato : 
basis convextuscula, laté perforata ; umbilico cavernoso, limine acuto, 
denticulato, prope columellam interrupto: apertura circularis ; colu- 
mella obliqua, acuta, antice dentata, emarginata ; labro albo et nigro 
articulato, intus sulcato ; fauce margaritaced. 
Trochus (Monodonta) atropurpureus, Goutp ; Proceed. Boston Soc. 
Nat. Hist., 111. 107. April 1849. Expedition Shells, 59. 
Anat elongated, angles of the foot dilated, behind pointed; disk 
of the foot cream-coloured ; head transversely oval; veil ochreous; 
cirrhi long, yellow; above striped with delicate, alternately slate- 
coloured and yellow lines; head transversely striped in the same 
manner ; eye-pedicles with finely lobed auricles. 
SHELL small, solid, depressed, ovate-conical, of a purplish-black 
colour: spire of five to six moderately convex whorls, separated by a 
deeply-impressed suture, and girt with uniform series of lines of ele- 
vated granules, of which there are six upon the smaller whorls, and 
about sixteen on the larger one, including the base: periphery of 
the last whorl very obtusely angular: base moderately convex, and 
largely perforated, the region surrounding the umbilicus white, and 
forming a sharp, denticulate margin to it, the tooth near the upper 
commissure of the aperture being mitch the largest where the circle 
of the umbilicus becomes incomplete, not attaining the columella, so 
that a part of the wall between the umbilicus and aperture is wanting: 
columella oblique, denticulate, a denticle above and below: aperture 
nearly circular, a little modified by the columella, at the base of which 
is an emargination: lip white, margined with articulated black and 
white spots; inner edge corrugate, striate: fauces pearly. 
Axis one-fifth of an inch; diameter three-tenths of an inch. 
Obtained at Pango-pango, island of Tutuilla, Samoa Group. 
Allied to T. pharaonis and T. canaliculata, in its habitus and um- 
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