44 W. Stimpson on the so-called Melanians of N. America. 
bottom of the pallial cavity. Its width anteriorly is about two- 
thirds that of the rostrum, but it becomes gradually narrower 
posteriorly. re consists of ‘fifty or more thin triangular lamina, 
the height of which is less than their length at the base of at- 
tachment. The supplementary or feather-shaped gill® is rudi- 
mentary, reduced to the simple mid-rib, which forms a short, = | 
linear, fleshy ridge between the left commissure of the mantle 
and the base of the principal gill, to which it is parallel. 
y specimens are not in sufficiently good condition to enable 
me to trace the position of the seta a (the “organ of vis- 
cosity ” of Cuvier) and its apert 
Sexual differences.—The Prowobe mvoliats Gasteropods are dis- 
tinguished as an order from the Pulmonates and Tectibranchs, 
by having the opposite sexual organs in different individuals, 
instead of existing together in the same individual. Prior to - 
the more recent investigations into the structure of the genital =| 
system in this order, the animals of a considerable number of =| 
the families composing it were ee cuppoeed to be hermaphrodites, 7 
For example, Cuvier states that the sexes are united in the mol- 
lusks composing his orders Scutibranchiata, Cyclobranchiata, and 
Tubulibranchiata. And SS some of the most recent authori- 
ties still continue to regard some of these animals as hermaphro- 
dites. Carpenter, in his “A sides ” published in 1861, ones that 4 
in the order rapes (in which he includes the Troc hide, | 
Turbinide, etc.) “the arrangements for the continuance of the 
species, instead of eee separated on different individuals, are 
united in the same individual, which is supposed to be capable | 
M - 
of self-impregnation.”* And Moquin-Tandon, in his work on 
the terrestial and fluviatile Mollusks of France, and inaspecial 
article, describes an organ in the generative apparatus of Valvata, = 
which he considers to be an arab toa gland.” So there | 
are said to be hermaphrodite Littorinz. 
But the Trochidz and Turbinide sad all of the Scutibranchi- 
ata are now known to have the sexes distinct; that the same is 
the case in the Cyclobranchiata, has been shown b y R. Wagner* 
and Milne Edwards;’ and that the Tubulibranchiata are not 
hermaphrodites, has ‘been established by the observations of 
von Siebold” upon Vermetus, the exactitude of which has been 
_® It should here be remarked, however, that the function of this organ is a matter 
‘controversy. Some have considered it a color gland. But it has been generally 
regarded as a supplementary gill; and in those genera in which it is most largely 
> ge aie as Buecinum, Natica, and Cyprea, it pestsiols has a branchiiform struc- 
I wih the to 
ture. I: regard it as a true gill, homologous with the right gill of 
ost same structure and apparently th the same — al orca if 
-* Smit fates for 1860, 
= —— tag ologie Bi, 1852), Pear 
= a — df . é : a rts 
