PARASITIC HABITS OF CRUSTACEA. 245 
that lives in the interior of the shell between the gills of the 
oyster, and is often cooked with that excellent bivalve. This 
is the Pinnotheres ostreum (Fig. 41), and is doubtless para- 
sitic in the oyster merely for the sake Fig. 41. 
of shelter, and probably does not in- 
jure the oyster unless by the irrita- 
tion that its motions might cause. But 
it is doubtless an unweleome guest, 
though the ancients had a notion that 
à similar species inhabiting the Pinna ENS as a sort of sen- 
tinel by giving notice of danger, and thus warned the Pinna 
when to close. Hence its name, which signifies Pinna-guar- 
dian. 
Another species, P. maculatum, lives in mussels ( Mytilus) 
upon our coast. Another lives at Panama in a species of 
Lithodomus, a shell allied to Mytilus, but which is itself 
parasitic, and lives in holes which it excavates in other shells 
and corals. "There are many other species of Pinnotheres, 
and allied genera, having similar habits. One fine species * 
lives in the Pearl Oyster (Margaritophora fimbriata) of the 
Bay of Panama. It often shares its secure pearly retreat 
with a curious slender fish, and with two other genera of 
Crustacea, very different from itself, resembling Seen 
or miniature lobsters in form. The most common of these is 
a new species-of Pontonia,f a genus previously known to be 
Pee Se pee) gti vu Dto CREDENS MM 
* Dignoll k , sp. nov., female. Body co covered with a very short and 
lose pubescence e, looking very ie like ating of mud. Carapax quite 
thiek and vic considerably broader than long, and strongly convex ; 
and gastric regions by 









v pair, where the daetyius is very long, almost straight, 
ite posterior pair the dactyli are long, straight, slender and pube 
1 Pontonia ma arita Smi oet d smooth 
; Smith, g and all the appendages 
k rg sp. nov. Body hace mad sbsder & thé up: 
naked. Cara: 
pex very broad, depressed 
a slender spine on the at the base of the antenne. Eyes small, the 
MON dir d the lla of the he antennule short, the inner ones 
. Anterior legs slen- 
er; the outer ones of about the same length, st 
