GASTEROPODA. 119 



panels, convexiusculis ; transversim striatis, striis tenuibus, aliquando crassioribus, distan- 

 tibus; anfractu ultimo ventricoso ; aperturd subovatd ; supernd acuminata; columella 

 depressd, obliqud. 



Shell very variable, more or less ovate, thick, strong, and imperforate, with an 

 acute apex; spire generally depressed, but sometimes elevated; whorls slightly 

 convex, transversely striated ; strise fine and small, sometimes coarse and elevated, 

 often ornamented, with coloured bands ; last whorl ventricose ; columella depressed 

 and oblique. 



Axis, 1 inch. 



Locality. Red Crag, Sutton, Bawdsey, &c. 



Mam. Crag, Bramerton, Thorpe, and Bridlington. 



Recent, British and North Seas. 



This shell appears first in the Red Crag, where it is by no means abundant ; but 

 in the estuary deposit of the Mammiliferous Crag it may be found in great profu- 

 sion. It is the most characteristic shell of that formation. This species may be con- 

 sidered as an arctic form, with a geographical range not very extended, while Turbo 

 rudis is given by Dr. Gould as an American species. I have seen nothing among 

 the numerous varieties from the Crag that could be fairly identified with the latter 

 species, the shell considered to be so in * Min. Conch.' being only a variety of L. 

 littorea. 



The principal difference in the specimens which I have considered as only 

 varieties of one species appears to be in the lengthening or shortening of the con- 

 voluted cone, with an occasional thickening or elevation of some of the more 

 prominent strise. The form of the aperture is invariably the same, but it differs 

 enormously in its proportions with regard to the axis of the shell. 



In my Catalogue it is stated that the presumed cause of these variations was a 

 more than ordinary alteration, and at various times, of the water in the estuary, 

 which these animals are supposed to have inhabited ; or perhaps the daily flow and 

 ebb of the marine tide might for some time leave them in a purer fresh-water 

 medium than was congenial to their nature, and this, probably, augmented occa- 

 sionally by the introduction of floods of fresh water or ice. The animals of this 

 species, with which the London markets are supplied, are obtained from the sea, 

 and are more uniform in character. 



Da Costa says, that the specimens of this species found on the shores of the 

 Orkneys, are four times the size of those brought into the London markets. These 

 shells are commonly called " Periwinkles," which is a corruption of petty winkle, 

 or whelk. In Suffolk they are known by the name of " Pinpatches." 



Fig. 14 is the normal or typical form of this species ; from a to h are considered 

 to be varieties, or mere monstrosities. Fig. 14 d is from the cabinet of Mr. Fitch. 



