184 BULLETIN OF THE 
few exceptions, — which may be assumed to belong to the “inflexible” 
group, — in those cases where a considerable number of individuals of 
one species were obtained by the “Blake,” the variation in form and 
sculpture is very wide, much more so than in most littoral forms. Owing 
to the absence of light, color in abyssal mollusks is almost wanting ; but 
in the species which possess it, as in some of the Pectens and Callio- 
stomas, the range and variety of coloration within the species is very 
wide. The tints are chiefly browns, pinks, and shades of yellow. The 
sheen and play of colored light presented by the pearly species are re- 
markably brilliant and fine. Among the archibenthal forms a notable 
number are characterized by squarish red-brown spots on a light-colored 
ground. I suspect that the abyssal mollusks are less active and ener- 
getic than their congeners of the shores. This is indicated by the 
looseness of the tissues, less favorable to prompt and violent motion 
than more compact muscular apparatus would be. The tenacious 
character of the mud forming the ocean floor, noticed by all explorers 
of the deeps, would also tend to make motion through it slow and dif_i- 
cult. The delicacy of the shells, the extreme fragility and tenuity 
which mark them, are inconsistent with liability to constant friction and 
collision, either from the motions of the animal itself or of the waters 
in which it lives. An exception may be noted in favor of the swimming 
mollusks, such as the squids and cuttlefishes, but the deep-sea repre- 
sentatives of these groups are far softer and less muscular than their 
shallow-water relatives. 
Much of the sculpture which is presented by the deep-sea species is 
particularly beautiful from its delicacy. There seems to be an especial 
tendency to strings of bead-like knobs, revolving strive and threads, 
and delicate transverse waves. It is particularly notable that many of 
the deep-sea forms, among all sorts of groups indifferently, have a row 
of knobs or pustules following the line of the suture and immediately 
in front of it. The representatives of the rock-purples, or Murices, a 
group which, in shallow water, frequent the rocks and stony places, and 
are there strongly knobbed or spinous, retain a similar character in the 
deeps, but the processes in question are extremely delicate or foliaceous, 
instead of being stout and strong. This is probably a reminiscence 
of the time when their distant progenitors were shallow-water animals. 
The groups which subsist upon other animals with a hard covering, 
so that they have to bore or break their way to their food, are much less 
numerous in the deep sea than those which feed upon soft tissues, or 
kill their living prey by bites with poisonous fangs. The latter, Towo- 
