28 The American Naturalist. [January, 
rather than merely for the sake of its faunal interest, these 
notes are written. 
The species occurs very commonly as a flesh-tinted scum on 
the abdomen or on the tips of the joints of the walking legs 
(pereiopods) of the Channel Crab Libinia emarginata. This 
crab lives abundantly a very lazy life in the deeper waters near 
the mouth of Oyster Bay and in the bays and sounds gener- 
“=, $ \ 
ally that connect with the Atlantic Ocean in the latitude of 
Long Island. If specimens of the crab be placed immediately 
upon capture in an aquarium, the hydroid, if present, can be 
seen as a fleshy fuzzy mass in the midst of the rather abund- 
ant hairy material that covers the creature on the ventral sur- 
face quite generally. The hydroid is thus a messmate of the 
crab, but there is no proof that I know of that the latter is in 
any way affected by the presence of this lowly companion. 
There is a disease of a certain fish caused by the presence of a 
parasitic hydroid described by Fewkes as Hydrichthys mirus 
