204 NATICID 2. 
operculigerous lobe long, cylindrical, bearing the operculum on 
its truncated extremity. Operculum claw-like, with a spiral 
nucleus situated near the internal or thickened border. 
Shell spiral, turbinate, imperforate; spire elevated, whorls 
rounded ; aperture oval, produced in front. 
The little animal wields its clawed operculum, apparently as a 
weapon of defense, with great dexterity, and skips and jerks 
about by means of its complex foot. 
GeMELLA, H. and A. Adams. 
Distr.—G. hyalina, H. and A. Ad. (Ixxxvii, 12). South Pacific. 
The foot is not unlike a broad or square-toed shoe in form, re- 
ceiving or bearing the remainder of the animal and the shell. 
The little animal creeps with great rapidity, and by hollowing 
the disk of its foot into a boat-form, like Limneea, it floats upon 
the surface of the seas. 
Operculum paucispiral, the lines of growth well-marked. 
Shell subglobose, thin, pellucid, not umbilicated ; spire small, 
compressed, whorls few, smooth ; aperture large, entire. 
Famity NATICID 2. 
Shell globular or oval, spire usually short, aperture semilunar, 
without canal or anterior notch, the outer lip sharp, the colu- 
mellar lip callous, more or less reflected over the umbilicus. 
Animal with small tentacles, which are lanceolate, wide apart, 
united by a veil; eyes usually absent, or very minute and placed 
beneath the tentacular veil; mantle enclosed ; foot much pro- 
duced in front, where it is furnished with a fold which covers 
the head and tentacles; operculigerous lobe very ample, par- 
tially enveloping the shell. Operculum paucispiral, corneous, 
or with an exterior calcareous layer. Dentition, 3°1°3 (xi, 31). 
The nidus of Natica (xvii, 95) is unlike that of any other 
mollusk in form and composition, being built up largely of the 
sand of the sea-bottom, formed into a partly circular form con- 
stricted into a neck above, the walls of which contain the eggs 
arranged in quincunx order. 
Narica, Lam. 
Distr.—A bout 200 recent sp. World-wide, and ranging from 
low-water to 90 fathoms. Fossil, 500sp. Silurian—; world-wide. 
N. Alderi, Forbes (1xiii, 41). NN. canrena, Linn. (xiii, 42). 
Shell subglobular, spire slightly elevated, aperture half-round, 
a spiral columellar callus entering the umbilicus. 
Animal blind, completely retractile within its shell. Oper- 
culum with an exterior calcareous layer. 
The animals of Natica (typical) move quickly; they are 
carnivorous and very predaceous, living in sandy places, where 
