GAMMARUS PULEX. 395 



of the toothless-backed fresh-water species, under G. 

 pulex, had evidently in view a littoral species : " Habitat 

 in maris 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 



