OF MOLLUSCA. 153 



setose ; the lateral vibracula are 3 ■ 3, setose, half-retractile ; bran- 

 chial plume minute ; operculum multispiral. 



The mantle of Gibbula lineata is even, but the pillar-lappet often 

 forms a branchial fold ; head-lappets two, small, suboval, lateral ; 

 the neck-lappets are only a continuation of the operculigerous lobes, 

 the one on the pillar side breaking into eight or ten dentations, the 

 outer one plain. — Clark, Moll. 309. 



14. Margarita. 



Shell subglobose, thin, polished or striated; axis umbilicated, 

 open ; aperture nearly circular ; pillar-lip ending in a point ; throat 

 iridescent. Operculum of many rather gradually enlarging whorls. 



1. M. helicina, Adams, Gen. Moll. t. 49. f. 60, operculum; Forbes 

 $• Hartley, B. M. t. C.C. f. 4. 



Lingual membrane of Margarita antarctica linear, transparent, 

 rather dilated in front. Teeth 00 * 5 • 1 • 5 * 00 ; central tooth elon- 



Fig. 83. — Teeth of Margarita antarctica. 



gate, dilated in front ; upper edge concave, very transparent ; inner 

 lateral 3*3 or 5*5, linear, bristle-like, arched, acute, rather far 

 apart ; middle lateral strong, transparent, with a strong transparent 

 apical hook ; outer lateral very numerous, crowded, slender, hooked 

 at the end (fig. 83). 



The skin of Margarita is reticulated. Tentacles hispid, with very 

 minute tubercles, channeled above, with a minute internal lobe. Eye- 

 pedicel free, short, united by a frontal veil. Foot with a large ante- 

 rior lobe and lateral beards, grooved above behind. — Loven. 



Prehensile collar of Margarita helicina distinct. Teeth 00'6* 1 'frOO; 

 the central thirteen subsimilar, strap-shaped ; apex recurved, denticu- 

 lated, the middle one rather the broadest ; lateral numerous, subu- 

 late, recurved at the tip. — Alder. 



ff Pillar-lip slightly twisted in front. 



15. Tegula. 



Shell elongate, top-shaped; axis imperforate, covered with a 

 callous deposit ; pillar spirally twisted, ending in a large prominent 

 tubercle in front. 



1. T. pellis-serpentis. 



The axis of this shell is rarely perforated. 



