GASTEROPODA. 119 



paucis, convexiusculis ; transversim striatis, striis tenuihus, aliquando crassioribus, distan- 

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

 depressu, 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; striae 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 profusion. 

 It is the most characteristic shell of that formation. This species may be considered 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 convoluted cone, 

 with an occasional thickening or elevation of some of the more prominent striae. 

 The form of the aperture is invariably the same, but it differs enormously in its pro- 

 portions 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 fi-esh-water medium than was 

 congenial to their nature, and this, probably, augmented occasionally by the intro- 

 duction of floods of fresh water or ice. Tlie animals of this species, -svith 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 k are considered to 

 be varieties, or mere monstrosities. Fig. \-\d\% from the cabinet of Mr. Fitch. 



