482 MAZATLAN tTNIVALVES 



rounded, in shape like Purpura ; sometimes extremely elonga- 

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

 the loose separate laminee of growth which pass over the siiture 

 connecting the whirls. When in fine condition, it has one 

 principal row of about 8 tubercles, spirally flattened, more or 

 less conspicuous ; and generally, anoth^ smaller row bslow. 

 "When these aie developed, and the first row smaller, the 

 resemblance to P. biserialis is remarkable. The whole surface 

 has crowded spiral striae, closely imbricated with not-obtuse 

 semicircular scales, crenulating the mai'gin. 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 strise, within and without. These 

 corrugate the muscular sear, 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 lonrj. 'OS, lon^. spir. *4, lat. "8, div. 80''. 



The largest sp. „ 2-5f), „ I'lS, „ Vl, „ 55'^. 



A scalaroid sp. „ 1'68, „ "92, „ I'OS, „ 40". 



Kah. — [New Holland ; Duclos. Kiener, &c. ?] — 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 

 growinc: from a stony bottom ; C. B. Adama. — La Paz, 

 Lieut. Greea. — 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. — 2230. the most effuse specimen, ( = Purpura, sp. 72, 

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

 found. — 22S1, 1 operculum. 



610. CaMA cosTATA, Blainv. 



Purpura costata. Blainv. Nowv. Ann. 3Iiis. 1832, p. 231, no. 63, 

 pi. 11, f. 8. — Kien. Icon. Conch, p. 61, no. 38, pi. 17, f. 51. 



? = Purpura diaderaa (Lam. teste Rue. in Ind.) Roe. Conch. Ic. 

 pi. 12, sp. 62, 1816.— Cuma d. S. ^ A. Ad. Gen. i. 134. 



Comp. Cuma calcar, Brod. in Mas. Cum. 



C. t. phos miniisve rhomb icd, spird plus minusvo elevatd ; 

 alhidd, intus interdum violasccnte, interdum pallide ochraced, 



