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 shorea 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 diffi- 

 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 striae 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, Toxo- 



