138 CRUSTACEA—PERACARIDA CHAP. 
tion, one species, P. femorata, being entirely marine, in the 
Arctic and North Atlantic, P. afinis inhabiting the Atlantic, 
and also freshwater lakes in Europe and North America, 
P. microphthaima being confined to the Caspian Sea, and P. loyt 
to Lakes Superior and Michigan. 
Fam. Gammaridae.—lIncludes fifty-two genera. The first 
antennae are slender, with the accessory flagellum very variable. 
The mandibles have a dentate cutting edge, spine-row, and molar 
surface, and a three-jointed palp. The first two thoracic limbs 
ave subchelate. This family includes a few marine, but mostly 
Th 
__ Abad 
Fic. 95.—Gammarus locusta, 6 (above) and @ (below), x 4. Abd.1, First abdominal 
segment ; 7, telson; 7, seventh free thoracic segment (=8th thoracic segment) ; 
U, third uropod. (After Della Valle.) : 
brackish and freshwater species. Crangony# 1s entirely subter- 
ranean in habitat, as is Miphargus, N. forelic occurring, however, 
in the deep waters of Lake Geneva. Both these genera are blind. 
Gammarus has thirty species, G. locusta being the common species 
on the North Atlantic coasts, and G, pulea the common freshwater 
species of streams and lakes in Europe. A number of Gammaridae 
inhabit the Caspian Sea, e.g. Boeckia, Gmelina, Niphargordes, etc., 
while the enormous Gammarid fauna of Lake Baikal, constitut- 
ing numerous genera, showing a great variety of structure, some 
of them being blind, belong to this family, eg. Macrohectopus 
(Constantia), Acanthogammarus, Heterogammarus, etc. 
