FRONT-GILLED GROUP 3343 



The olives (Olividce} are mostly cylindrical shells, often beautifully orna- 

 mented with markings of various patterns, and always having a highly glossy or 

 enameled appearance. The aperture is narrow or notched in front, and the 

 columella is not strongly plaited as in some of the families which follow 

 (Afarginellidce) , but there are numerous, slight, oblique folds, some of which pass 

 round the base or anterior part of the shell, which is thus marked off from the rest of 

 the surface into a distinct area. The animal has a very large foot, capable of cover- 

 ing the shell to a great extent, pointed behind, and with its anterior portion 

 (propodium) divided into two lobes. The head is small, with pointed, slender 

 tentacles, and the eyes about midway along their outer sides. The mantle is pro- 

 duced in front into a slender appendage, which protrudes with the breathing siphon 

 through the notch of the aperture; posteriorly it terminates in a thread-like process, 

 which passes up the channeled suture of the spire. There is no operculum. The 

 olives are very active, and burrow in the sand in search of bivalves; and are some- 

 times seen in countless numbers, the sands at low tide for miles being covered 

 with them. Although about one hundred and fifty to two hundred species, mostly 

 tropical, have been described, a few extend to more temperate seas as far north as 

 Japan, and southward to Patagonia. The olives are frequently used in the manu- 

 facture of shell ornaments. The genus Olivella differs from the typical Oliva in 

 having neither tentacles nor eyes, and the spire of the shell is longer and more 

 pointed. Ancilla, another important genus, comprises a number of polished species, 

 which are nearly always of a uniform white, yellow, fawn, brown, or reddish 

 color, and without the markings of the olives. 



The family Harpidce contains but a single genus, the well-known harp shells 

 (Harpa). These are strong, broad, ventricose structures, highly colored, and 

 adorned with numerous curved ribs, running parallel with the outer lip of the 

 aperture. The columellar margin is smooth, and covered with a thin brilliant 

 callus. The animal has an enormous foot, which is not wholly retractile within 

 the shell; and when disturbed it not unfrequently casts off the hinder part. 

 About ten species are recognizable. They occur in the Red Sea, many parts of 

 the Indian Ocean, Philippine islands, South Sea islands, Panama, and on the 

 west coast of Africa and at Ascension island. The members of the family 

 Marginellidce are mostly small, some very minute, but many of them have 

 very beautifully colored and highly polished shells. Nearly all the tropical, and 

 many of the finest and most valued are inhabitants of the West- and South- 

 African coasts. They are mostly ovoid, or subconoidal in form, with rather con- 

 tracted apertures, slightly notched in front; the outer lip is involute and thickened, 

 and the columella has a few oblique plaits upon the lower or anterior portion. 

 There is no operculum; and, as in the majority of the volutes, the radula has only 

 a central row of teeth. In Pseudomarginella from Goree, on the west coast of 

 Africa, the shell is identical in every respect with Marginella glabella of the 

 same locality, but the mollusk and its operculum are said to belong to the Buc- 

 cinidce. 



Nearly all the species of the family Volutidce have large showy shells, and some 

 of them, on account of their extreme beauty and rarity, realize very high prices. 



