188 
TROCHUS. TOP-SHELL. 
extremely fine and close-set circular liner,; 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, pcrlaceous within; the perfora¬ 
tion small, deep, olten 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 an inch; height rather more. 
From the circumstance of the grooved aperture and 
slightly toothed lip, wc suspect that the next species was 
a larger or a foreign specimen of this shell. 
Western coasts, and Dublin bay. v. v. 
5. Trochus dnereus. Grey Top-slull. 
Lister, pi. G3 3. f. 2 1— 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 : 
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 , 6 to 11. 
' 6 . Trochus crassus. Thick Top-shell* 
Da Costa, pi. 6. f. 7— Dorset Cat pi. 17. f. 3 and 7—» 
Donovan , pi. 71. 
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 
