THE ARTHEOPODA OF THE DEEP SEA 129 



of 9 inches (fig. 15). Stenetrium hasiuelli, again, is 

 larger than any of the shallow-water species of the 

 genus, and the same remark applies to the deep- 

 sea species of the genus Ichnosoma, while lolantlie 

 acanthonotus, from a depth of nearly 2,000 fathoms, 

 is considerably larger than most of the shallow-water 

 Asellidt^i. 



There is another very common character of deep- 

 sea Crustacea that is also well exemplified in the 

 group of the Isopods, and that is the extraordinary 

 length and number of the spines covering the body. 



I have already referred to this character in the 

 supposed deep-sea Copepod Pontostratiotes ahyssicola^ 

 and I shall have again to refer to it in treating of the 

 Decapoda and other groups of the Crustacea. 



Besides its enormous size Bathynomus possesses 

 some other characters that may be correlated with 

 its deep-sea environment. The respiratory organs are 

 quite different from those of other Isopods ; instead 

 of being borne by the abdominal appendages, they 

 are in the form of branched outgrowths from the 

 body-wall containing numerous blood-lacunas, and 

 the appendages simply act as opercula to cover and 

 protect them. The eyes of the Bathynomus too are 

 remarkably well developed, each one bearing 4,000 

 10 



