482 MAZATLAN UNIVALVES 
rounded, in shape like Purpura; sometimes extremely elonga- 
ted, the whirls scarcely touching. It is known in all stages by 
the loose separate lamin of growth which pass over the suture 
connecting the whirls. When in fine condition, it has one 
principal row of about 8 tubercles, spirally flattened, more or 
less conspicuous; and generally, another smaller row below. 
When these ate developed, and the first row smaller, the 
resemblance to P. biserialis is remarkable. The whole surface 
has crowded spiral striz, closely imbricated with not-obtuse 
semicircular scales, crenulating the margin. This, as well as 
the shell generally, is marked with blackish brown. Canal 
recurved, twisted, generally forming an umbilical chink. 
Operculum purpuriform, dark chesnut brown, with extremely 
minute transverse radiating stris, within and without. These 
corrugate the muscular sear, which has rounded costx of 
growth. The few specimens found in the Mazatlan collection 
were for the most part much worn, and often the location of 
Ostrea conchaphila and Balani. A very young depresed sp. 
measures long. ‘98, long. spir. *4, lat. °8, div. 80°. 
The largest sp. Be hs ey os 14S) te een. 
A sealaroid sp. rea BOOS : "OR SOs eOS serene. 
Hab—[New Holland; Duclos, Kiener, &c. P|—Panama; on 
rocky places at low water; Cuming.—Do. ; abundant from 
half tide nearly up to high water mark of neap tides, on 
rocks and on lower parts of trunks and about roots of trees 
growing from a stony bottom; C. B. Adams.— La Paz, 
Lieut. Green.—Mazatlan; very rare; L’pool Col. 
Tablet 2257 contains 2 sp. normal state, one with operculum 
in situ.—2258, 1 sp. spire elevated. — 2259, 1 sp. periphery 
rounded.—2260, the most effuse specimen, (= Purpura, sp. 72, 
C. B. Ad.) Between these extremes, a regular gradation was 
found.—2281, 1 operculum. 
610. Cuma costata, Blainv. 
Purpura costata, Blainv. Nouv. Ann. Mus. 1832, p. 231, no. 63, 
pl. 11, f. 8.— Kien. Icon. Conch. p. 61, no. 38, pl. 17, £. 51 
?=Purpura diadema (Lam. teste Rve. in Ind.) Rve. Conch. Ic. 
pl. 12, sp. 62, 1846.—Cuma d. H. & A. Ad. Gen. i. 134. 
Comp. Cuma calear, Brod. in Mus. Cum. 
C. t. plus minusve rhombicd, spird plus minusve elevata ; 
albidd, intus interdum violascente, interdum pallide ochracea, 
