MUREX. ROCK-SHELL. 91 



the volutions from six to ten ; when the spires are few the 

 shell has a more conical appearance, and the aperture is 

 often a little dilated or more rounded, and the canal shorter 

 and more or less truncate at the end ; and when the outer- 

 lip has the back rib close to the edge, it is thicker, and the 

 internal crenatures are not visible. 



The gradations of these varieties are so clear and appa- 

 rent, that at present we have no doubt of their being the 

 same species. In his description of M. gracilis, Montagu 

 has not noticed the notch on the lip ; but in his Supple- 

 ment, at p. 1 14, he has particularly pointed out this mark 

 as its essential distinction from M. accinctus. w. v, 



8. Murex accinctus. Girdled Rock-shell. 



Laskey, Wern. Soc. i. pi. 8. f. 14. 



Shell taper, with six or seven ribbed volutions ; the ribs 

 slightly angulated or elevated in the middle of each volu- 

 tion, and crossed by fine spiral thread-like lines : color yel- 

 lowish-white, with an obsolete brown band on the middle of 

 the larger volution, which continues up the shell at the 

 base of the smaller ones ; this band, by the help of a glass, 

 is observed to be formed of four or five contiguous thread- 

 like lines of that color : aperture oblong, with a short ca- 

 nal, the outer-angle of which is entire. 



Montagu observes that it differs from M. gracilis in the 

 aperture and the canal, and in wanting the notch at the 

 upper angle of the outer-lip : it however so exactly cor- 

 responds with the smaller species of that shell, where the 

 aperture is proportionately wider, the canal shorter, and 

 the notch hardly formed or not very visible, that there is 

 much doubt of its being specifically distinct : length four 

 lines ; breadth one. 



In the Firth of Forth, where only one specimen seems to 

 have been taken, by Captain Laskey. 



9. Murex attenuatus. Taper Rock-shell. 



Montagu, pi. 9. f. 6. 



Shell slender, tapering to a very fine point, yellowish- 

 white : spires eight, with nine equidistant strong ribs, 

 which are rather undulated, but not striate across; the volu- 

 tions hardly raised, and separated by a very fine line only : 



aperture 



