4 GENUS HARPA 



pointed. The liver, which is voluminous, forms a great part of 

 the convoluted portion, and extends almost throughout the spire. 

 The heart and the auricle are very much developed, contained 

 in a pericardium, and situated at the base of the branchiae. The 

 cerebral ganglion is broad and flattened ; it sends out numerous 

 nervous filaments which ramify over the whole body. The penis 

 of the male is considerable, like that of the Buccina, and 

 situated upon the same side. 



This genus, very remarkable for the beauty and freshness of 

 the shells which it contains, belongs mostly to the Indian seas, 

 where they are pretty common, and upon the shores of certain 

 islands of the tropical coasts. They are found in the crannies 

 of rocks, or upon pebbly bottoms, whose great irregularities 

 render the means of fishing for them ineifectual. Quoy and 

 Gaimard think that they usually inhabit rapid and deep waters. 



The animal is very active, but surrounded by numerous ene- 

 mies ; at the approach of danger it enters its shell, like the other 

 mollusca, but cannot entirely draw in its foot; and the part 

 which remains without, firm and muscular, almost closes her- 

 metically the aperture of the shell, and thus protects all the soft 

 parts. Nevertheless, if the danger which threatens it should 

 be imminent, as a last resort, it contracts with much force this 

 portion of the foot exposed to peril, breaks it and rids itself 

 of it. In this situation it presents to its enemies only the back 

 of its covering, being able to apply its aperture to the ground. 

 It is probable it owes its power of rupturing its foot to the pre- 

 sence of a large canal containing water which exists in this part. 

 This is the opinion of Quoy and Gaimard. 



In consequence of this an operculum would be useless to it, 

 for it would be liable to be carried away by the rupture of the 

 foot. Therefore, it is not possessed. These observations are 

 due also to the philosophers we have previously quoted. 



Some system-making authors have sought to establish on the 

 operculum, general rules of analogy between the groups ; but this 

 character is too superficial to serve for the great divisions, or 

 the approximation of groups into families. Many shells, pro- 

 vided with an operculum, are united by all the other characters 

 which distinguish them, to species, in which the operculum, on 



