GAMMA RUS PULEX. 
393 
douces des ruisseaux et des fontaines ; ” or where 
GeofFroy says of his species that it is “ trouve commime- 
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 w r as 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 
marinae 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 lie 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. 
