826 THE AMERICAN NATURALIST. | [Vor. XXXV. 
some unusual shock has been given to the free rim of the 
shell, for the mantle to contract in crenulate lines, a tendency 
which during the descent of the tetrabranchs may well have 
been seized upon by selection and made of use in the formation 
of the specialized margins of the septa. And from this stand- 
point the recent markings may be regarded as related to 
the curiously expressed lines on the ancient shells. They 
seem of entirely too regular a character, as close examination 
shows, to be interpreted merely as lines marking the repair of 
the free lip of the shell. Such lines of repair do, indeed, occur 
and are common, for the shell-lip is delicate and often apt to 
be injured in an animal with the evident habits of nautilus. I 
have in mind one instance when the shell had been repaired, 
after the lip had been crushed badly ; in this case the main 
fracture passed backward from the rim of the lip to a distance 
of 4.5 cm. f 
General Appearance of the Living Animal. — The first glimpse 
at a living specimen showed it at the bottom of the vessel in 
which it had been brought, its position upright somewhat as 
shown in the present Fig. 6. If the vessel is sufficiently large - 
the animal is usually found with its back (Z.e., its aboral pole, 
so to speak) pushed as far as possible into a corner. And 
if several specimens are thus confined they will often be found 
to have backed away from one another as far as possible. 
They remained thus almost motionless sometimes for hours ; 
at other times they will exhibit active movements and subside 
quite suddenly. The color of the animal one gets little idea of 
from preserved specimens. The general color of the exposed 
parts, hood excepted, is white, clean, opaque, almost the same 
tint, in fact, as the body of the shell. The latter was in every 
case I observed brilliantly clean. The face of Nautilus, then, 
is white, as is also the dorsal fold of the mantle, which rises 
into sight within the concave hinder rim of the hood and covers 
when extended the jet-black portion of the coil of the shell. 
The dorsal surface of the hood, as one would infer from pre 
served specimens, is of a brownish color. Looking at this 
surface for the first time in a living specimen, one is given the 
impression that it has been spattered with burnt umber, raw 
M 
