468 MAZATLAN UNIVALVES 
Voluta tenebrosa, (Mawe) Wood, Ind. Test. Suppl. pl. 4, f. 38. 
Olivella undatella, H. § A. Ad. Gen. i. 146. 
Comp. Oliva zonalis, Whe. in Zeit. f. Mal. 1847, p. 183, no. 25 ; 
non Lain. 
This species varies, as usual, in the elevation of spire and 
the comparative breadth : but its principal changes are in 
colouring ; passing from pure white to rich purple or more 
usually with zigzag or undulating markings, pink on a white 
ground, or, (normally) with various shades of dark olive. The 
spiral band occupies more or less of the back, at a greater or 
less angle. Although the animal remained in many of the 
specimens, sufiiciently fresh to swell out in water, no trace 
of operculum was found. ‘The largest of the specimens 
measures long. ‘68, long. spir. "18, lat.°3, div. 70°. 
A broad sp. ih BS rf os Ka mrs di iter hie 0) 
Hab.—Acapuleo, Humboldt & Bonpland.—Panama; in sand 
and on mud banks at low water; Cuming.—Do. very rare, 
C. B. Adams.—Mazatlan ; common; L’pool & Havre Coll. 
Tablet 2138 contains 5 sp. pure white.—2139, 5 do. slight 
markings of pink.—2140, 5 do. pink markings stronger.—2141, 
5 do. well developed.—2142, 5 do. markings fine and close.— 
2143, 5 do. pink passing into olive. 
Tablet 2144 contains 5 ‘sp. white with rare spots of olive.— 
2145, 5 do. olive spots more developed.—2146, 5 do. with broad 
white band.—2147, 5 do. olive markings undulating.— 2148, 
5 do. zigzag.—2159, 5 do. passing into general olive. 
Tablet 2150 contains 5 sp., undulations absent or very faint ; 
gray with white spiral band.—2151, 5 do. spiral. band dark, 
gray passing towards purple.—2152, 5 do. dark purple.—2153, 
5 do. purple changing into olive.—2154, 5 do. lighter.—2155, 
5 do. dark olive changing into light.—2156, 5 do. light olive. 
Tablet 2157 contains 5 sp., undulations more or less distinct ; 
olive tinged with orange.—2158, 5 do. markings light, faint 
olive.—2159, 5 do. more distinct.—2160, 5 do. distinct.—2161, 
5 do. dark olive.—2162, 5. do. white groundwork appearing.— 
2163, 5 do. white in larger spots.—2164, 5 do. colour darker.— 
2165, 5 do. rich olive.—2166, 5 do. shading into purple. 
Tablet 2167 contains 4 sp. mended after fracture, colour 
changing.—2168, 3 sp. shewing variations of form.—2169, 2 do. 
spiral band varying.—(In all, 154 sp. with an appreciable dif- 
ference between every two.) 
