PURPURA. 277 



lpwards ; the last occupies from two-thirds to five-sixths of 

 the shell : suture rather slight, deeper towards the apex : mouth 

 oval, somewhat contracted hy the pillar ; its length is from 

 one-half to two-thirds of that of the sjDire : canal deep, exhibit- 

 ing outside a corresponding and oblique notch : outer lip curved, 

 bevelled on the inside to a rather sharp edge (which is slightly 

 indented by the ridges in young shells), notched or tubercu- 

 lated within, sloping above from the periphery : inner lip broad, 

 continuous with the outer lip at the upper corner of the mouth : 

 pillar broad and smooth, angulated where the canal begins ; 

 between the lower part of the pillar and the basal ridge there 

 is an oblique cavity as in Trichotropis : operculum dark horn- 

 colour ; lines of increase distinct ; nucleus placed nearer the 

 base than in the middle of the outer side ; it exhibits under- 

 neath four or five irregularly elliptical layers, being apparently 

 the marks of annual growth. L. 1*5. B. 1. 



Yar. 1. imbricata. Longitudinal striae more developed, and 

 forming a flounce-like ornamentation. P. imbricata, Lam. An. 

 s. Vert. vii. p. 244. 



Yar. 2. major. Larger and having a longer spire. L. 2-5. 

 B. 1-25. 



Yar. 3. minor. Smaller, more strongly ridged, with a 

 shorter spire and wider mouth. L. 0*75. B. 0-5. 



Monstr. Spire reversed, scalariform, or having scarcely any 

 canal. 



Habitat : Gregarious everywhere on rocks and stones-, 

 exposed to the tidal waves of 



" the sea, that fleets about the land, 



And like a girdle clips her solid waist." 



Here it gets abundance of food, which mainly consists 

 of mussels, limpets, and sessile barnacles. It sometimes 

 finds its way into deeper water. The 1st variety was 

 dredged by Mr. M f Andrew on an oyster-bed from 4 to 

 7 f. in Rhoscollyn Bay, near Anglesea ; Mr. King, the 

 natural-history dealer, also found it near Holyhead, and 

 Dr. Knapp in the Firth of Forth. Var. 2. Off the 

 Mumbles Head, near Swansea, in 18 f. (J. G. J.). 

 Var. 3. Burrafirth Caves, Shetland (J. G. J.). A speci- 



