392 
GAMMARIDiE. 
animals now found in it, (and which are known at this 
day only to inhabit the extreme north), could have lived 
in the same latitude as the south of Sweden. The 
evidence of these fresh-water lakes suggests that similar 
changes in the relative position of sea and land may have 
been the cause of our having fresh-water Crustacea nearly 
allied to marine species in our rivers and inland streams. 
A fact, however, recorded by Hosius with regard to the ha- 
bitats of the three fresh-water species of western Germany 
would seem to discountenance the idea that these animals 
can adapt themselves to any great change of situation. 
“ Inter loca, qum habitant, multum interesse mihi videtur; 
G. puteanus [Niphargus p.~\ tantum in puteo, G. pulex non 
nisi in rivis rapide profluentibus atque minime profundis, 
G. fluviatilis [Rosel’s species] in aquis solum stagnanti- 
bus aut lente manantibus ac profundis versatur. Nun- 
quam has ultimm species una mihi occurrerunt, nec si aquae, 
in quibus commorantur , inter se conjunctae erant . Dum 
enim, ut exemplum afferam, in piscina Popp els dorrfi ana 
G. fluviatilis solus reperitur, in rivo, qui e montibus 
hanc in piscinam effunditur, solus G. pulex versatur. 
Idem quoque mihi aquas prope Godesbergam perscrutato, 
probabile videbatur, ubi rivus, qui a Marienforst in 
planitiem defertur, tantum G.pulicem colit, dum instagnis 
cum rivo coliserentibus solus G. fluviatilis versatur.”— 
Dissert, de Gammari Spec. p. 18. 
Taking this statement of the diversity in the habitats 
of the two species of Gammarus , as here restricted, 
into consideration, we anticipate that Rosel’s tooth- 
backed species will yet be found in some of our 
ponds and stagnant waters, although it has not hitherto 
been detected. We are also hence enabled to identify 
the descriptions of various writers, from the habitat in 
which the specimens were found ; thus, where Latreille 
says that his Gammarus pulex is found, “ dans keaux 
