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 branchie. 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 imeffectual. 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 lable 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 
