BRITISH STALK-EYED CRUSTACEA. 359 
that of the following species; its lateral margin is armed with 
stout spines, of which two large ones protect the eye-stalks, and 
two others, still larger, form the bifid rostrum. 
The carapace is ornamented with spines and tubercles, inter- 
spersed with tufts of a remarkable hair-like process, which we will 
allude to more fully in the description of Pisa Gibbsii. These 
tufts afford lodgment to the spores of marine life, so that it 
is not unusual to find specimens of P. tetraodon to which are 
attached zoophytes, such as Plwmularia falcata, Alcyoniwm digi- 
tatum, and others; also sponges, such as Halichondria panicea, 
but as the following species is much more liable to this 
remarkable embellishment, we will describe individual specimens 
when dealing with P. Gibbsiz. 
The legs of Pisa tetraodon are stout and armed with hairy 
tubercles. They taper off after the first joint and are furnished 
with extremely sharp curved claws, which are capable of being 
clenched back upon the next joint, so that the hold of the animal 
is rendered very secure; in fact, its habits in this respect corre- 
spond to those of many parasites which live on the hair of animals, 
and require a firm mode of attachment. This similarity of 
development is of considerable interest, and when we consider 
that the habits of this genus are extremely retiring and sedentary, 
this means of a secure anchorage is accounted for. 
The anterior pair of legs are as usual developed, in the male, 
into a formidable pair of forceps. Bell observes that these legs 
do not attain to this size until the animal is adult, so that males 
which are nearly full grown may have them equal in size to the 
anterior pair of the female. In fact, specimens are sometimes 
met with which have these legs fully developed, and yet are of 
smaller size than others whose corresponding limbs are quite 
immature. 
The abdominal somites are seven in number, narrow in the 
males, but so broad in the female as to be almost circular, and 
thus capable of affording protection to a large mass of ova. The 
somites are divided vertically by a broad ridge or keel, with a small 
tubercle on each somite. 
The antenne in this species are studded with clubbed hairs; 
the external pedipalps are broad, and the eyes, which are very 
little broader than their peduncle, are capable of being turned 
back for protection into their orbit. 
