GAMMARUS PULEX. 
395 
of the toothless-backed fresh-water species, under G, 
pulex, had evidently in view a littoral species : “ Habitat 
in mar is littora frequentissimus saliens, retia destruens, 
piscibus infestans, in brachiis ulcera caussans.” These 
interesting peculiarities of habit are not in the slightest 
degree attributable to our fresh-water species; on the 
other hand, the G. locusta of Fabricius evidently com- 
prised both a littoral and fresh-water species, " etiam 
ssepe in fontibus et fossis stagnantibus.” The G. pulex 
of Latreille, Hist. Nat. Insectes, &c., vol. vi. p. 316, 
is a fresh-water species, the description of it is not, 
however, precise enough for discrimination ; the habitat 
indicates a species found in running streams, but the 
figure (pi. Ivii. fig. 1) is copied from Rosel’s figure of the 
tooth-backed species. 
There is, however, fortunately, no confusion in the 
descriptions and figures of De Geer, Zenker, Burgers- 
dijk, Hosius, Gervais, Koch, and Zaddach ; and in em- 
ploying the name of Pulex for the present species, as 
used by De Geer and subsequent authors, we are 
adopting the strict rules of nomenclature, as well as 
employing a term^ which recalls the strong resem- 
blance which exists between the appearance and 
general movements of our common flea and the fresh- 
water shrimp now before us, except that the latter is 
unable to leap. 
During the winter months these animals bury them- 
selves in the mud of the rivulets and streams which they 
frequent. On the first warm days of spring, however, 
they reappear, when the larger individuals may generally 
(as indeed throughout the summer) be seen carrying a 
smaller one beneath the body, holding it tightly by 
means of the fingers of its two anterior pairs of hands. 
These smaller individuals are the females, and this 
curious courtship, for such it is, lasts seven or eight 
