76 
Verrill (1893) has described a Stylochus zebra and notes that all 
his specimens collected off New Haven, Conn., were found in the 
canals of dead shells of Fulgur, that were occupied by Eupagurus 
pollicaris. Other specimens taken in Vineyard Sound were living 
in the same manner. 
Wheeler (1894) presents the following notes: „Possibly Stylo¬ 
chus zebra, Verrill, may be somewhat parasitic. This beautiful 
species is not uncommon at Woods Hole in the dead shell of Lu- 
natia heros tenanted by hermit crabs and invested with Hydrac- 
tinia. Whether the planarian merely selects the Lunatia shell as 
a hiding-place or bears some definite relation to the hermit crab, 
I am unable to decide". v. Graff 1903 says with regard to this 
species: „bietet aber nichts in ihrer Organisation, was als Folge 
ihrer eigentiimlichen Lebensweise zu deuten ware. Wenn dieser 
nicht von den Frassabfallen profitiert, so ware zunåchst daran zu 
denken, dass vielleicht der hier abgesetzte Laich besser geschiitzt 
sei, als in anderen Lokalitåten“. This latter supposition is, in my 
opinion, hardly acceptable, as such a condition would probably 
have been recognized by the observers, and we know further that 
Hoploplana inquilina leaves its host for the deposits of eggs (Surface 
1907). St. zebra, though being a Stylochus, has a rather elongated 
shape. The anterior location of the pharynx and its relative shortness 
are also unusual for a Stylochus. The same is valid for the situation 
of the mouth in front of the centre of the pharyngeal pocket. A 
Stylochus species with the mouth in the first third of the body 
deviates apparently from the common type. This moving of the 
mouth is perhaps a result of its stay with the Pagurids. As to 
the finer structures of this species, we are rather unacquainted. 
In the two species treated here are some features which may 
possibly be interpreted as established in connection with the as¬ 
sociation with the hermit crab. 
It has already been pointed out with regard to Euprosthiostomum 
that the sucker has been enlarged and also removed to the post- 
erior end of the body, while in other Prosthiostomids it is more 
or less subcentrally placed. This increase in the power of attach- 
ment, as well as the altered location of the sucker, is of clear 
advantage during the new modus of life. In Emprosthopharynx 
opisthoporus the adhesive zone is regarded as a kind of substitute 
