482 MAZATL'AK UNIVALVES 



rounded, in shape like Pnrpura ; sometimes extremely elonga- 

 ted, the whirls scarcely touching. It is known in all stages by 

 the loose separate laminae 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 aie developed, and the first row smaller, the 

 resemblance to P. biserialis is remarkable. The whole surface 

 has crowded spiral strise, closely imbricated with not-obfcuse 

 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, wifli extremely 

 minute transverse radiating striae, within and without. These 

 corrugate the muscular scar, which has rounded costae 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. '93, long. spir. *4, lat. '8, div. 80. 



The largest sp. 2 '56, 1'18, 1'7, 55. 

 A scalaroid sp. 1*63, '92, 1'OS, 40. 



Hat. [New Holland; Duclos, Kiener, &Q. ?] Panama ; on 

 rooky places at low water ; Coming. 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, 

 Ijieut. G-reen. ^lazatlan ; very rare ; IS pool Col. 

 Tablet 2257 contains 2 sp. normal state, one with operculum 

 in situ. 2258, 1 sp. spire elevated. 2259, 1 sp. periphery 

 rounded. 22GO, the most effuse specimen, ( = Purpura, sp. 72, 

 C. B. Ad.) Between these extremes, a regular gradation was 

 found. 2261, 1 operculum. 



^ 610. CUMA cosTAfA, Blainv. 





 Purpura costata. Blainv. Nouv. Ann. Mus. 1832, p. 231, no. 63, 



pi. 11, f. S.l&en. Icon. Conch, p. 61, no. 38, pi. 17, f. 51. 

 ? = Purpura diadema (Lam. teste Rue. in Ind.) Rve. Conch. Ic. 



pi. 12, sp. 62, 1846. Cuma d. H. fy A. Ad. Gen. i. 134. 

 Cornp. Cuma calcar, Brod. in Mus. Cum. 



C. t. plus tninusve rhomb icd, spird plus minusve elevata ; 

 albidd, inius interdi'/ni violascsnte, interdum pallide ochracea, 



