TROCHUS. 309 



same character as the capitular ones. There are two small, 

 very dark, suboval head-lappets, situate at the inner sides of 

 the tentacula. What are called the neck-lappets are only 

 continuations of the operculigerous lobe, the one on the 

 columellar side breaking into 8-10 long dentations; the outer 

 one is plain ; both are of a flake-white, mixed with pale green 

 on both sides. 



The animal is littoral, and plentiful, though locally distri- 

 buted. 



A singular character is attached to this species, which I 

 have not observed in any other Trochus. The animal either 

 casts the operculum, or is deprived of it by the attacks of 

 enemies, perhaps from its own pulli, white masses of which, 

 in the genial season, I have seen deposited on the foot, and 

 they may possibly feed on and destroy it ; however this may 

 be, numerous examples are found with the opercula in various 

 stages of development and renewal, but never resembling the 

 original : this is a curious fact, which I can at present scarcely 

 account for on rational grounds. The renewals and repara- 

 tions form irregular spiral, oblique and elliptical curves, or, 

 instead of the sixteen normal volutions, often only show two 

 grossly spiral ones, as in the Littorina littorea. I have many 

 such in my collection. I may observe, that, however the 

 sculpture of the area may be varied, the operculum always 

 retains the circular form. 



The species of this section that have not occurred in a 



living state are, 



T. MILLEGRANUS, Philippi. 

 T. millegranus, Brit. Moll. ii. p. 502, pi. 66. f. 9, 10. 



? T. ALABASTRFM, Beck. 

 T. alabastrum, Brit. Moll. ii. p. 497, pi. 66. f. 7, 8. 



T. EXIGUUS, Pulteney. 

 T. exiguus, Brit. Moll. ii. p. 505, pi. 66. f. 11, 12. 



T. STRiATUs, Linnaeus. 

 T. striatus, Brit. Moll. ii. p. 508, pi. 66. f. 5, 6. 



T. CONULUS, Linnaeus. 

 T. conulus, Brit. Moll. ii. p. 495, pi. 73. f. 1, 2. 



