UNIVALVES. 



PLATE XLVII. 



Genus. TROCHUS. 



Character. Shell conical, spiral, the aperture depressed crosswise, and slightly 

 quadrangular, the perpendicular axis inclined to the base. 



Species. 

 No. 1. Trochus acuminatus. Shell of a dark purple, spotted with tessellae in 



the form of tiling ; mouth prismatic, green, and red, form ventricose, and 



tapering gradually to the summit. A native of New Zealand. 

 No. 2. Trochus decarinatus. Shell green, streaked across with sharp furrows, 



between each fold of the spire a very deep furrow ; the mouth prismatic, red, 



and blue. This elegant shell is also a native of New Zealand. From Dr. 



Lettsom's Museum. 

 No. 3. Trochus altus. Shell red, variegated with white; mouth yellow, verging 



to brown ; the folds punctuated, and slightly carinated. This shell, which is 



very rare, was discovered at Botany Bay. 

 No. 4. Trochus bicolor. Shell white, streaked with green and brown ; mouth 



brown. A native of New Holland. From a specimen in Dr. Lettsom's 



Museum. 

 No. 5. Trochus apiaria. Shell woven of white and green in the manner of a 



bee-hive, which it much resembles in form ; mouth brown. A native of 



Van Diemen's Land, and differing from No. 4 materially in the number of 



the folds of the spire. 

 No. 6. Trochus melissus. Shell of a pale honey colour, with ribs at each joint 



of the spire transversely placed, and slightly spotted ; mouth brown. A 



native of Madeira. 



REMARKS. 



The genus Trochus forms a curious family, consisting of shells of a triangular form, which, 

 when placed upon a flat base, have their spire constantly leaning to one side ; they resemble 

 in a great measure the Patellae, except that they have an internal staircase, or helical spinal 

 process, which the Patellae are without. These shells are natives of almost every country 

 and coast, and present an infinite number of individuals, highly interesting for the pearly 

 appearance and prismatic colours of the mouth, which seems as if very narrow, and is 

 almost hid, by being placed, as it were, at the bottom of the shell ; it differs from the 

 Turbo genus in being more square ; the Turbo has also an orbicular mouth, and the folds 

 of its spire are more distinct, and projecting in their form. The largest specimens are 

 found chiefly near the Torrid Zone. The discoveries in the South Seas have added con- 

 siderably to the different varieties hitherto known. 



