188 TROCHUS. TOP-SHELL. 



extremely fine and close-set circular lines ; the base of the 

 larger volution with a slight keel-like circular ridge : color 

 grey or purplish-brown, with sometimes a yellowish cast, 

 rarely spotted with white at the top of each volution,, with 

 numerous longitudinal obscure oblique waved lines or spots : 

 aperture a little angular, perlaceous within ; the perfora- 

 tion small, deep, often divided in the middle by an elevated 

 ridge, giving it the appearance of having a double groove, 

 with frequently a small tooth-like projection on the pillar- 

 lip : diameter about a quarter of aninch ; height rather more. 



From the circumstance of the grooved aperture and 

 slightly toothed lip, we suspect that the next species was 

 a larger or a foreign specimen of this shell. 



Western coasts, and Dublin bay. v. v. 



5. Trochus cinereus. Grey Top-shell. * 



Lister , pi. 633. f. 21 Da Costa, pi. 3. f . 5 Donovan^ 

 pi. 155.f. 2. 



Shell thick, strong, with five tumid spires, rather 

 pointed at the top, with numerous raised circular strife j 

 color grey, with close-set blackish lines ; the base varie- 

 gated with blackish streaks which run lengthways and 

 across, pearly and of a light greenish cast about the per- 

 foration, which is large, deep, and cylindrical ; the pillar- 

 lip with two slight teeth, and two transverse furrows : 

 about double the size of the former. 



A very doubtful species. 



B. Not perforated at the base, G to 11. 



6. Trochus crass us. Thick Top-shell. 



Da Costa, pi. 6. f. 7 Dorset Cat. pi, 17. f . 3 and 7-r 

 Donovan, pi. 1\. 



Shell strong, thick, conic, pointed, smooth covered with 

 a coarse coat, under which it is of a fine iridescent perla- 

 ceous color : spires five or six, rather tumid, separated by 

 a faint spiral line ; the larger volution with a few obsolete 

 wrinkles near the mouth, and often slightly notched or 

 jagged on the line of junction ; color dull greyish-brown, 

 with numerous purplish zigzag lines ; inside perlaceous, 

 with a black band round the margin ; the pillar-lip and 



about 





