120 THE NAUTILUS. 
gard for right will admit. Acknowledging frankly the great de- 
fects of the eccentric naturalist’s work, its value and genius are 
still considered by Call to be very considerable. There can be no 
doubt that in the appreciation of natural groups, Rafinesque had 
great insight, as his biographer claims; but still we can hardly en- 
dorse the statement: “considered as a whole, the conchologic work 
of Rafinesque was remarkably well done.” From some acquaint- 
ance with that work, we would rather call it remarkably badly 
done, and only saved from worthlessness by certain glimmers of 
genius, in the ability to grasp natural groups. Some facts of value 
could have been obtained had Mr. Call corresponded more freely 
with Philadelphians, as here Rafinesque spent many years. Among 
other things, the statement in regard to the Poulson collection of 
Rafinesque’s Unionide on p. 109, would not have been made. This 
collection was collected and labelled by Rafinesque, was procured 
by Tryon from Poulson’s estate and is now preserved in the collec- 
tion of the Academy of Natural Sciences of Philadelphia. 
Asa whole the volume seems remarkably free from mistakes of 
any kind, considering the difficulty of the subject. The typography 
issuperb. The proof-reading is almost perfect, though we note a 
very few slips, such as “ profligate” for prodigal, on p. 75. It is 
printed on fine paper, with wide margins, and is altogether a beau- 
tiful piece of book-making. We trust it will find a place on the 
shelves of conchologists and naturalists generally, and lead to a 
more just appreciation of this great though erratic genius. 
THE MecuanicaL CAusE or FOLDS IN THE APERTURE OF THE 
SHELL OF GaAsrropopa, By Wm. H. Dall (Amer. Nat., Nov., 
1894).—The plicz and folds found in the aperture and throat of 
gastropod shells are explained by the wrinkling of the mantle when 
retracted into the gradually narrowing caliber of the shell, and 
pressed between the solid foot and the shell wall. The semi-fluid 
secretion of which the shell-lining is built up is exuded from the 
whole surface of the mantle, but becomes rubbed off where the sum- 
mits of mantle-folds press against the shell, gradually accumulating 
in the interstices between these folds. It is found that in shells 
having the ridges extending far inward, the adductor muscle is at- 
tached far within; in those having no folds, or only at the margin 
of the aperture, the adductor is attached to columella lower down. 
The deeper this attachment, the greater the distance over which 
the mantle is drawn, and consequently the greater its folding by 
compression, and the more emphatic the shell-ridges deposited by it, 
