GAMMARUS PULEX. 393 



douces des ruisseaux et des fontaines ; " or where 

 GeofFroy says of his species that it is " trouve commune- 

 ment dans l'eau courante des petits ruisseaux," we are 

 convinced that each alludes to the species of De Geer, 

 found only in running rivulets, although both have 

 copied Rosel's figure of the tooth -backed species found 

 only in still and stagnant water. 



The earliest notice we meet with of a species named 

 G. fluviatilis occurs in Ray's work on Insects, p. 44, 

 where he loosely describes an insect under the name of 

 Pulex fluviatilis, found " in aquis calidis in specu 

 Custozse prope Vincentiam, in Italia, ubi nulla anima- 

 lia vivunt.'' This animal was probably a species of 

 Niphargus, but Ray added a few words to his description, 

 which might thence also be supposed to include our fresh- 

 water species, " quae in nostris rivulis sunt non saltant ut 

 marinas sed incurvant se et natant podicem exerendo 

 satis celeriter." We next find Linnaeus in his Iter 

 (Eland. , pp. 42, 96, speaking of " Cancer Pulex fluviatilis 

 dictus, Suecis Marta, Scanis Sandhare. Habitat ad littora 

 maris vulgatissimus, frequens rodens retia, conficiens 

 sceleta piscium, natat in dorso/' characters and names 

 which evidently apply only to our Gammarus locusta. 

 We next find Rosel employing the term Astacus fluvia- 

 tilis in a generic sense * for several distinct kinds of 

 long-tailed Crustacea, of which he gives excellent 

 figures, namely, the cray-fish, the shrimp, and a fresh- 

 water species of Gammarus, for which the specific name 

 has been subsequently retained, and which is dis- 

 tinguished at once by having the middle of the hind 

 margin of each of the segments of the tail armed with 

 a strong tooth. This has been named G. Roselii by 



* Just as he employs the term " Cimex aquaticus " for the general heading 

 of the plates of all the species of Water Hemiptera which he figures, including 

 at least six modern genera. 



