TROCHUS. 323 



black) in the line of growth ; in some specimens the streaks 

 are interrupted and give a speckled appearance, or there is a 

 greenish tint, and in others the apex is reddish : spire bluntly 

 pointed : whorls 7, gradually enlarging, flattened, all but 

 the two apical ones, which are rounded: suture very .slight and 

 inconspicuous : mouth obliquely squarish : outer lip rather thin : 

 inner Up short, broad and thick, undistinguishable from the 

 pillar ; it is slightly reflected above, and notched below by a 

 small blunt tubercular tooth, as in the last species : inside 

 silvery and iridescent, except towards the margin, where it is 

 frosty- white and thickened by an indistinct angulated rib ; 

 the young are slightly umbilicate : operculum as in T. Monta- 

 cutC L. 0-35. B. 0-3. 



Monstr. Scalariform ; whorls convex, each having a keel- 

 like ridge in the middle, and separated from the one next to 

 it by a deep suture ; base rounded. 



Habitat : Laminarian zone (especially on Zostera 

 marina), from low-water mark to 15 f., in the Channel 

 Isles, Dorset, Devon, Cornwall, Cork, Baltimore, and 

 Bantry. Dublin Bay (Turton). The monstrosity was 

 found by Mr. Hockin at Falmouth, and by him kindly 

 presented to me ; it is similar to that of T. Montacuti. 

 The present species has only been noticed as fossil in 

 the Sicilian tertiaries (Philippi). Recent on the coasts 

 of France, Portugal, Spain, Italy, Algeria, the Adriatic, 

 Madeira, and the Canaries, from the shore to 20 f. 



The animal of this rather common species does not 

 appear to be known. The shell differs from T. Monta- 

 cuti in its larger size, remarkably flattened whorls and 

 base, and in having a greater number of spiral ridges. 



In all probability the T. striatus of Linne was in- 

 tended for the next species — if indeed that is not a 

 variety of the one which I have now described. Gmelin 

 and his followers named the present species T. erythro- 

 leucos, Da Costa T. parvus, Donovan T. conicus, and 

 Deshayes T. delictus. 



