176 LECTURES ON MOLLUSCA. 



with, a Muricoid operculum. Their favorite haunts are the rocky 

 shores of South Africa, Australia, and New Zealand; Metula being an 

 American and East Indian group. 



In the same way Anachis represents the ColumbeUas; from which 

 the shell is known simply by having a more elevated spine and trans- 

 verse ribs. 



Family Buccinid.e. (Whelks.) 



The genus Buccinum of Linnaeus contained all the shells with a 

 notched base : a heterogeneous group, most of which have been moved 

 off, step by step, to other families and genera; leaving only a few 

 species, mostly from the boreal seas in each hemisphere, to keep up 

 the ancient family name. The Whelks are very closely related to the 

 Murices, from which they differ chiefly in having a thin, oval opercu- 

 lum, with the nucleus a little out of the centre. The true Buccinum 

 has a notch for the breathing tube, and Stromhella (a shell common in 

 the Norwegian seas, but still so rare near England that good specimens 

 sell for ten dollars) a short canal. The Columbelke, which are very 

 pretty little shells, extremely abundant in both oceans of tropical 

 America, are still but little known in their economy, but belong by 

 operculum to this family. They have their mouths so twisted by 

 teeth, that the foot and operculum has to go in and out sideways. 

 Perhaps this accounts for the operculum being so often broken and 

 abnormally repaired. It is a curious fact that whatever be the form 

 of the operculum in the different tribes of predacious mollusks, when- 

 ever it has been broken and has to be repaired by the animal, it always 

 takes a simple oval shape with concentric layers, the nucleus being in 

 the middle. In one place on the English coast there is found a race of 

 Buccinum undatum (the common whelk of the English and American 

 coasts) which perpetuates a very abnormal condition. They have two 

 small opercula of more or less irregular shapes, but each of concentric 

 elements. Probably their remote ancestor met with an accident, and 

 has transmitted her mode of repairing the fracture to her descendants. 



Family Pyrulidje. 



The shells, of this group run into those of Fusus by insensible gra- 

 dations; but the animals present a well-marked difference. The neck 

 (not the snout, as in the Strombs) is very long, the proboscis being 

 still further extensile. The head and tentacles are small in proportion. 

 Many of these shells are very large. The Pyrula melongena and P. 

 patula, inhabiting respectively the Atlantic and Pacific shores of 

 tropical America, are eaten by the natives. In the genus Hemifusus 

 are two of the largest living Gasteropocls, the H. colosseus and probos- 

 cidalis of the East Indies. 



Family Purpurid.e. 



The animal of Purpura differs very little from that of Buccinum and 

 Murex; but the operculum is formed on a very peculiar plan. Outside 



