926 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
of Purpurifera, was proposed by Lamarck with the view of associating a 
small but characteristic group of mollusks, that had been admitted for 
the most part under the common title of Buccinum costatum or harpa. 
They approximate to the Buccina and the Purpure, but as their shells 
exhibit an accurate peculiarity and distinction, the genus has been sanc- 
tioned by subsequent naturalists. Even before the present form of clas- 
sification was introduced, the different species were often called by the 
names of ‘‘ the David’s Harp,” ‘‘ the imperial Harp,” ‘the rose Harp,” 
and so forth; the determination of the species is indeed still a matter 
of controversy, and we find it difficult at present to give an opinion. 
Before we attempt to dispute with Deshayes the propriety of considering 
the Harpe ventricosa, imperialis, articularis, striata and conoidalis as mere 
varieties of one and the same species, we must think well of, and con- 
sider for ourselves the momentous question,—what constitutes a spe- 
cies? The anatomy of the Harpe, described first by a M. Reynaud, and 
afterwards by Quoy and Gaimard, has been so fully set forth by Kiener, 
that it is only necessary for us to notice a remarkable peculiarity in the 
foot of these mollusks, described by the enterprizing malacologists of the 
Astrolabe. It is represented as being so large and muscular as to be quite 
incapable of being contained within the shell, and the animal is said to 
have the power, when irritated or in any dangerous emergency, of spon- 
taneously divesting itself of so much of this muscular disc as it is unable 
to protect within the shell. This fact at once accounts for the absence of 
an operculum, and only shows how little importance can be attached to 
that organ for the purposes of classification. 
The ridges which adorn the shells of the Harpe are evidently analogous 
to the varices of those of the Canalifera, each forms in its turn the mar- 
gin of the aperture, and, like them, may probably be deposited to protect 
the edge of the shell during a period of rest, the greater multiplicity of 
ribs indicating the more periodical growth of the shell. 
The shell of Harpa may be described as being oval, ventricose, and 
emarginated at the base, whilst the spire is short, with the apex rather 
elevated and acute; the whorls are more or less longitudinally ribbed, 
and the ribs, which run exactly parallel with one another, are highly 
