100 ^Zoological Society : — 



Fam. Trochid^. 

 Tegula pellis serpentis. Panama. 



Operculum horny, thin, orbicular, of many narrow, gradually en- 

 larging whorls ; foot folded together longitudinally when contracted ; 

 eyes on thin elongated pedicels ; tentacles linear, sheathed at the 

 base by the inner part of the base of the eye-pedicels ; frontal lappet 

 none ; lateral fringe of left side distinct, with three beards just be- 

 neath it ; lingual membrane elongate, broad ; teeth in ten longi- 

 tudinal series, in arched cross rows, elongate, with a rounded apex ; 

 lateral teeth linear, crowded, arched at the end. 



Order Pleurobranchiata. 

 Fam. Aplysiad^. 

 Aplysia DEPiLANS ? Gcnoa. 



The small, polished, subglobular spiral (sinistral?) nucleus or 

 apex of the older shell is, with the subapical part of the shell, co- 

 vered with a membranaceous reflection of the inner lip over its sur- 

 face, which is only slightly adherent to the surface of the shell and 

 nucleus, and easily removed from it, but which gradually becomes 

 thicker ; the top of the shell appears to be absorbed, or more or less 

 obliterated in the older specimens. 



According to Mr. Woodward, Mr. Hancock has observed in the 

 adult specimen two or three shells one within the other, like the Loli- 

 gines or Sea slaves. 



Fam. Tylodinad^. 



Tylodina PUNCTULATA=r. Rttfinesquii, Philippi. 



Lingual membrane very broad, brown ; teeth small, uniform, very 

 numerous, in very numerous longitudinal lines, forming straight con- 

 tinued uniform lines across the membrane, with an indistinct central 

 line ; the tentacles subulate, slit on the outer side ; the lips are 

 produced and acute on each side, and twisted, leaving a slight 

 cavity on the outer side of the tip ; the mantle is thin, free all 

 round the edge and slightly thickened just within the margin, 

 rather thicker and more free over the front of the back ; the gill 

 is single on the hinder part of the right side just under the mantle, 

 attached the whole of its length on the inner side by a central ridge 

 to the side of the body ; the outer side is furnished with a rather 

 thick, somewhat zigzag central vessel, giving out pinnated vascular 

 branches, nearly alternating with each other on each side of the great 

 vessel ; the foot is larger than the mantle and shell, expanded, rounded 

 behind, truncated in front and slightly emarginate in the centre 

 under the mouth ; the sexual aperture not visible in the specimen 

 in spirits. Shell conic, patelloid, thin, slightly pearly within, with a 

 thin, hard, horny periostraca, which is produced beyond the edge of 

 the shell, and rndiately coloured, in the dry state brittle, hard, and 

 contracted ; the apex (of the shell) subcentral, with a rather pro- 

 duced polished top, nucleus subglobose, with a shghtly convex spire 



