186 TRGCHUS. TOP-SHELL. 



The rounded outline of the front margin, the want of the 

 ear-shaped appendages, the internal rib, and more espe- 

 cially the accessorial dorsal valves, strongly mark this spe- 

 cies from the two last. It may also be observed that the 

 hinder part is closed when the valves are placed together, 

 in consequence of their rounded outline. 



Thrown up on the Devonshire coast, v. m.~ 



TROCHUS. TOP-SHELL. 

 Shell with a single valve, spiral, more or less 

 conic : aperture somewhat angular or rounded, 

 and contracted transversely ; pillar placed ob-r 

 liquely. 



A. Perforated at the base, 1 to 5. 

 P. Imperforate at the base, 6 to 11. 



1. Trochus Magus. Tuber ded Top-shell Fig. 64. 

 Lister, pi. 641. f. 32 Pennant, pi. 83. f. 4~Da Costa^ 



pi. 3. f. \-Donovan, pi. 8. f. I Dorset Cat. pi. 16. f. 1, 2. 



Shell with five or six tumid spires, a little depressed, 

 encjjng in a fine point, marked with fine circular ridges, 

 well defined by a deep separating line, and a raised rib, 

 round the base of each $ the top of each volution rather 

 flattened,, and surrounded with a row of obtuse tubercles 

 or short ribs seated close to the ridges, and most conspi- 

 cuous on the larger ones : color dull white or brownish, 

 often marked with irregular spots lines or undulations of 

 scarlet, pink, pale purple, or chesnut-brown : aperture a 

 little compressed and somewhat angular, the pillar a littlq 

 prominent in the middle, with a large and deep perfo- 

 ration. When the outer coat is removed it presents the 

 richest iridescent perlaceous hue : diameter from an inch 

 tp an inch and a half, and about as much jn height. 



On most san4y shores, v. v. 



2. Trochus umbilicatus. Purple-tipped Top-shell. 

 Pennant, pi. 83, f. 3 Da Costa, pi. 3. f. 4 Donovan^ 



pL 74, middle fig. Dorset Cat. pi. 16. f. 7, S. 



Shell with five spires, which are hardly raised or distinct 



