A. E. Verrill — North American Cephalopods. 
269 
state when the animal died. Candal fin transversely rhomboidal, 
or broad spear-shape, about one-third wider than long ; its breadth 
usually less than half the length of the mantle ; the posterior borders 
are nearly straight and form nearly a right angle at the posterior 
end ; the anterior margins are somewhat convexly rounded, and the 
front margin extends, at the sides of the body, considerably forward 
beyond the insertion of the fin. Ratio of fin-length to mantle-length 
1 : 2 - 48 to liS'OO (the latter in the young ones). Average propor- 
tions in eight adult specimens : of fin-length (from insertion) to length 
of dorsal side of mantle, about 1 : 2*55 ; breadth of fin to length of 
mantle, average, 1 : 1 *90 ; length of head (dorsal edge of mantle to 
base of arms) to mantle-length, average, 1 : 7T5. 
The head is large, well-rounded ; the exposed portion is shorter 
than broad, its breadth about equals that of the body, in ordinary 
contraction ; its sides, in the region of the eyes, are somewhat 
swollen; the under surface is flattened, and has a deep excavation 
in front, semi-circular, or rather semi-elliptical, in outline, to receive 
the dorsal half of the siphon-tube, which fits into it closely. 
The sides of the head, back of the eyes, have a rather prominent, 
transverse ridge, back of which the head suddenly narrows, to the 
neck. The transverse ridges curve backward slightly and meet on 
the dorsal side of the head, where they are less prominent. Three 
thin, lamelliform, erect folds of the skin extend backward from the 
transverse ridge, on each side of the head; of these the middle or 
lateral one is about in line with the lower eye-lid ; the upper one is, 
at its origin, about midway between the latter and the median dorsal 
line, but its posterior edge bends downward and joins that of the one 
below; the lowest of the three is shorter and curves upward, and 
finally joins the middle one, at its posterior edge. These folds form, 
therefore, in connection with the transverse ridge, two well-defined 
lateral areas or facets, of delicate and probably very sensitive integu- 
ment, placed just in front of the mantle-opening, on each side, where 
they must be bathed by the inflowing currents of water. It seems 
probable to me, therefore, that they are the seat of a special sense, 
analogous to, if not identical with, that of smell. They are, also, 
closely connected with the organs of hearing, and may be of some 
service in concentrating sound-vibrations. A small pore is situated 
within the lower facet. 
The pupils are round and the eyes are large, though the opening 
between the lids is usually rather small, especially in alcoholic speci- 
mens. In these the aperture is usually contracted to a small obliquely 
transverse, irregular-triangular form, or even to a narrow oblique slit; 
