204 NATICIDyE. 



operculigerous lobe long, cjdindrical, 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 dexteritj'^, and skips and jerks 

 about by means of its complex foot. 



GrEMELLA, 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 Limnsea, 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. 



Family NATICID^E. 



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 usuall}^ 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. 



Natica, Lam. 



Distr. — About 200 recent sp. World-Avide, and ranging from 

 low-water to 90 fathoms. Fossil, 500 sp. Siluriau — ; world-wide. 

 N. Jlderi, Forbes (Ixiii, 41). N. caiu-ena, Linn. (Ixiii, 42). 



Shell subglobular, spire slightl_\' 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 quickl}^ ; the}^ are 

 carnivorous and very predaceous, living in sandy places, where 



