OF MOLLUSCA. 95 



c. Gills of a few, twelve to fifteen, lamince in regular descending 

 spiral series on the left side of the mantle-cavity. Operculum 

 distinct. Mouth of shell contracted, moderate, roundish 

 (pp. 78, 86). 



* Operculum spiral. 



Fam. XII. PLANAXID.E. 



Rostrum elongate. Tentacles subulate. Eyes sessile, basal, ex- 

 terior. " Gills in several lines," laminar. Mantle edge simple, 

 with a recurved siphon in front. Shell conical, solid, spirally 

 striated ; aperture oblong, with an anterior notch ; inner lip concave, 

 flattened. Operculum ovate, subspiral. 



Marine. 



a. Planaxina. Opercular mantle simple. Amphibious. 



1. Planaxis. 



Shell conical ; spire acute ; mouth oblong ; inner lip concave, 

 simple ; outer lip grooved within. Operculum ovate. — Adams, Gen. 

 Moll. t. 34. f. 2 a. 



1. P. pyramidalis. P. sulcatus, Quoy, t. 24. f. 6. 



2. P. nigra, Quoy, t. 24. f. 3, cop. Adams, t. 34. f. 2. On sea- 



shore on stones and plants, often left dry by the tide. 



Lingual membrane of Planaxis sulcata with seven teeth, 3 • 1 * 3 ; 

 central with a recurved apex, three-dentate, central largest ; inner 

 lateral rather broad, with a recurved apex, rather oblique, and with a 

 tooth on its outer edge ; outer straight, one-third the width of the 

 inner, with a slightly recurved apex. 



2. Quoyia. 



Shell conical, turrited, solid, spirally striated ; mouth small, ob- 

 long, with a small notch in front ; outer lip simple ; pillar-lip thick- 

 ened, rather flattened, concave, with a deep notch in the centre. 

 Operculum horny, ovate, thin, subspiral. 



1. Q. decollata, t. 24. f. 4, cop. Adams, t. 34. 



The foot of Quoyia is small, ovate, folded across, and crumpled in 

 front ; body quite simple on the sides. Rostrum short, ringed. Ten- 

 tacles slender, conical, far apart at the base ; eyes on short tubercles 

 at their outer base. Mantle simple, with a groove at the left angle, 

 without any appearance (when in spirits) of a distinct siphon as 

 in Planaxis. Operculum half-ovate, subspiral, of one and a half or 

 two whorls ; nucleus subapical. 



The shells only differ from Planaxis in having a large groove 

 on the hinder part of the inner lip, which is continued up the pillar, 

 (and is equally to be observed in the young shell,) and in the very 

 small size of the anterior canal. The operculum is said to have a 



