LECTURES ON MOLLUSCA. 31 



the head to protect it as it burrows in the sand. There are three 

 divisions in the family, of which the types are Oliva, Ancilla and Harpa, 

 and are thus characterized : 



Shell compressed, smooth : pillar plaited : suture chan- 

 neled : a tail from the side of the mantle occupying the groove. 

 ANCILLIN^E. Without shell channel and mantle tail. 

 HARPING. Shell ventricose, with varices pointed at the suture. 



The Olives are among the best known and most beautiful of shells. 

 They are found plentifully in all tropical seas, especially in the islands 

 of the Indian and Pacific oceans. They are fond of burrowing in wet 

 sand in quest of bivalves ; and can dart through the water with toler- 

 able rapidity, by expanding and flapping their fleshy foot. They are 

 very rapacious ; and the larger kinds are fished by hooks baited with 

 flesh. The shells are heavy, painted in beautiful patterns and highly 

 polished. The colors are often very variable in the same species ; and 

 as the shape of the shells is generally pretty uniform, there is great 

 difficulty in discriminating several of the kinds. The pillar-lip is not 

 plaited, as in the Yolutes and Mitres ; but there are numerous spiral 

 folds, of which the foremost unite and travel round the base of the spire, 

 forming a band of different color. 



In the Olivdlas, which are all small shells, living in vast shoals on 

 each side of tropical America, the spire is elevated and the mouth ex- 

 panded at the base. The foot is not so large ; and the typical species 

 have a very small operculum, which is however wanting in Lampro- 

 doma. In Agaronia the shell is even wider, and very thin. The back 

 is destitute of polish, and is therefore not so much immersed in the foot. 

 It frequents the west coasts of America and Africa, and is found in the 

 Eocene strata. In ScapJmla the shell is distorted by an enormous lump 

 at the suture. 



The Ancillas are polished shells, generally of a uniform white, fawn, 

 or brown color, without pattern. They are particularly plentiful in 

 Africa, and in the Eocene strata. In Dipsaccus which has, aid San- 

 della which has not, a winding umbilicus, the spire is elevated, arid the 

 spiral band round the base of the shell ends in a rudimentary tooth. 

 In Anaulax the shell is not polished outside, and the shell is thin and 

 wide-mouthed, like Agaronia in the last group. 



The Harps form a small but well-marked group ; of which the species 

 are so like each other that even the Messrs. Adams did not attempt to 

 subdivide them. They all have ventricose shells, with varicose ribs at 

 regular intervals, which may be sharp or flattened on the same speci- 

 men. They are painted brown in beautifully penciled patterns, with 

 shades of pink and white ; and on trie pillar is a large callosity, formed 

 by the olive-like foot of the animal. It is said that the creature will 

 part with its tail, rather than be caught ; after the manner of the 

 Italian lizards. In the London Clay is a curious fossil, the " Buccinum 

 stromboides' ' of authors, which forms an interesting transition between 

 the Harps and the Ancillas. It has only rudimentary varices ; but 

 their pointed tops remain. The general shape, and the lump on the 

 pillar, formed by the animal's foot, which is too large to enter the shell, 

 show close relations with the true Harps. 



