264 DR JOHNSTON'S DESCRIPTIVE CATALOGUE OF THE 



purple ; base circularly striate, flattish ; aperture subquadrangu- 

 lar, the pillar concave, pearly. Height ^ths ; the breadth T 8 ths. 

 Dillw. Rec. Sh. 799. 



Hob. Berwick Bay, not common. 



The shell is sometimes of a uniform white colour, when it has been described 

 as a distinct species under the name of " Trochus Lyonsii ;" and besides 

 this there are in our Bay two varieties ; in one the whorls are slightly 

 concave, and the base is covered with the circular impressed striae ; in 

 the other the whorls are even, and there are only two or three striae at 

 the pillar, and two near the margin, leaving the intermediate space per- 

 fectly smooth. Operculum thin, round, and circularly striate. 



Snail of a more or less deep brown colour, which is often disposed in patches 

 or irregular streaks, covered with small tubercles, and furnished on each 

 side with four slender retractile filaments, originating from a free mem- 

 branous border that garnishes the sides, the back concave and smooth : 

 mouth shortly proboscidiform, furnished with two small corneous jaws : 

 tongue long, linear, armed as usual wifeh minute prickles arranged in 

 regular series : tentacula setaceous, pale, quadrangular, with a dusky 

 line along the upper angles, and rough with minute papillae when viewed 

 through a good magnifier : eyes on distinct pedicles at the external 

 bases of the tentacula : margin of the collar crenate or sinuate : foot ob- 

 long, tapered posteriorly, the margin crenulate, the disk straw -yellow, 

 more or less tinted with red or flesh-colour. The edges of the foot can 

 be brought together so as entirely to conceal its disk. 



** Base umbilicate. 



2. Tr. cinerarius, shell conical, obtuse, yellowish or bluish-grey, 

 with numerous narrow purplish stripes ; whorls six, flat, spirally 

 striate ; the base flattish and the umbilicus deep ; aperture white, 

 perlaceous, subquadrangular. Diam. of base T B 5 or T ^ths; height 

 the same. Dillw. Rec. Sh. 779. 



Hab. Between tide marks, very common. 



The spire is more or less raised, the suture more or less distinct, the base in 

 some more 'deeply striated than in others, and the umbilicus in young 

 shells wider than in the old, in which it is almost obliterated ; but among 

 these varieties there are none with characters sufficiently marked to jus- 

 tify their elevation to the rank of species. Operculum circular, horny, 

 thin, concentrically striate, with a membranous border. 



The body and tentacula of the snail are finely marked with black transverse 

 lines, which become reticulated on the sides : tentacula two, slender, 

 setaceous : eyes on distinct footstalks at the external base of the tenta- 

 cula : mouth striated with black lines, armed with a pair of oblong 

 pointed cartilaginous jaws, and a ribbon-like tongue roughened with 

 acute prickles set in transverse curved lines : sides of the body furnished 

 with a ciliated membrane, underneath which protrude several long ten- 

 tacular filaments, which issue from tubular sheaths, and are retractile : 

 foot elliptical, yellowish, the margin fringed with very short fleshy fila- 

 ments, visible only with a magnifier. Our children call the shell Silver- 

 bucktes or Silver- Willies: they do not eat the snail. 



During the summer we often find a spawn on the fronds of sea- weed deposi- 

 ted in the form of a small ring, and of a cream colour. I believe this to 

 be the spawn of Tr. cinerarius. The ring is gelatinous, firmly adherent, 

 and contains innumerable ova, each separately laid in the centre of its 

 own gelatinous vesicle. 



