APPENDIX II 451 
slender form (Hricthonius difformis) inhabits the delicate tubes of 
a hydroid, while a third (Hyperia medusarum), as its name signi- 
fies, lives in the stomach cavity of a jellyfish. The Euthemisto 
is a surface-swimming amphipod, and in sufficient numbers forms 
an acceptable meal for hungry fishes, as examination of their 
stomachs has proven. Gammarus locusta, the common amphipod, 
or scud, is the most noticeable species of the shore, being very 
abundant between tide-marks. These creatures are of an olive 
brown or light chestnut-brown colour, much like that of the Fucus 
they inhabit. They skip about on their sides, and on entering 
the water swim rapidly with the back downward or sideways. 
The isopods, unlike the amphipods, are flattened above, and 
are usually of a uniform width throughout their length; in many 
cases all their legs are about the same size, whence the name 
“isopod.” They also have sessile eyes and are usually of small 
size, the largest ones in the Labrador fauna being the two Mesi- 
dotea, which are about three inches long and taper at the posterior 
end to a sharp point. The most slender form is Arcturus baffini, 
which may attain a length of nearly two inches, with antenne 
even longer. Several species are parasitic, as the fish-louse, ga 
psora, which lives on the skin of the cod and halibut; the shrimp 
parasite, Phryxus abdominalis, a hemispherical, distorted little 
lump of an isopod occurring under the abdomen of various species 
of Spirontocaris and Pandalus; and a similar but smaller form 
which attaches itself to the schizopod, Mysis oculata. The last 
two isopods exhibit great sexual dimorphism, the females being 
vastly larger than the males and of wholly different appearance. 
Other parasites belong to different orders of Crustacea. 
The copepods live mostly on the external surface or in the gill 
cavity of fishes, to which they cling by means of claws and sucking 
disks. They are represented by Lepeophtheirus salmonis, parasitic 
on salmon and sea-trout. This species is distinguished in the 
female by a metallic lustre and by long, slender egg strings. An- 
other species is Lernea branchialis, variety sigmoidea, in which the 
female is fixed in one position for life, having lost all trace of appen- 
dages save those which fasten her to the host, while the male is 
reduced to minute size, and, although capable of motion, adheres 
to some part of the body of the female. 
Occasionally a hermit-crab is infested with one of the Rhizo- 
cephala (Peltogaster), parasites which are allied to the Cirripedia, 
or barnacles, but are degenerate forms with saclike, unsegmented 
bodies without limbs; their antennze are modified into rootlike 
processes, which bury themselves in the host, from which they 
derive nourishment. 
The barnacles reported from Labrador all belong to the sessile 
