This fact does not accord with Agassiz's* conclusions from an examination of the 

 fishes of Lake Superior, all of which he regarded as distinct from the species of Europe, 

 yet it is paralleled in the case of some fresh-water mollnsca, while many of the terres- 

 trial animals, and especially the plants, both land and fresh water, are common to the 

 northern parts of both countries. Whether these forms are to be considered distinct 

 species, or only varieties of their marine allies, is a question on which I will not now 

 pretend to offer an opinion, as I have had no opportunity for examining authentic 

 specimens from the North Atlantic. Whether or not they have been derived from 

 ancient marine species left in the lake basins by the recession of the ocean, is, in either 

 case, in the present state of our knowledge, a difficult question, and one upon which 

 the investigation of the deep-water faunas of the lower lakes, and especially of Lake 

 Champlain, which we know to have been connected with the ocean at a recent geolog- 

 ical period, and hence to have a derivative fauna, would throw much light. Among 

 the other deep-water forms, there is no evidence whatever of derivation from marine 

 species. The insect larvse, all the worms, the Fisidium,i\ud the Hydra, are most eminently 

 fresh-water forms, while the Ostracoda and Copepoda, as groups, are inhabitants of 

 both fresh and salt water. 



The main facts of the bathymetrical distribution of the species are presented in the 

 following table : 



Names. 



Cottus Franklini 



Chironomus larvae 



Ephemerida? larvae 



Phryganeidae larvae 



Hydrachna 



Mysis relicta 



Pontoporeia affinis 



Crangonyx gracilis 



Gamniarus lacustris 



Asellus tenax 



Cladocera 



Ostracoda 



Copepoda 



Lumbricus lacustris 



Saenuris abyssicola 



Saenuris limicola 



Cbirodrillus larviformis. 

 Cbirodrillus abyssorum. 



Tubifex profundieola 



Nephelis fervida 



Nephelis lateralis 



iythyobdella punctata .. 



Procotyla fluviatilis 



Limnaia 



Physa 



Planorbis parvns 



Yalvata sincera 



Sphaerium 



Pisidium virginicum. . . . 



Pisidium abditum 



Pisidium compressum .. 



Pisidium, sp. nov 



Hydra carnea 



Depths in fathoms. 



4-8 10-17 30-50 00-100 100-140 140-169 



(?) 



(?) 



* Lake Superior, its physical character, vegetation, and animals, compared with those of other and 

 similar regions. 



