706 EEPOET OF COMMISSIONER OF FISH AND FISHERIES. 



Bathy metrical distribution of species. 



I have already alluded to the meagerness of the deep-water fauna of 

 the lake, and' to the uniform character of the bottom everywhere below 

 30 to 40 fathoms. Although our knowledge of the fauna of the lake is 

 still very imperfect, enough facts have been presented to show that 

 very few, if any, of the species which inhabit the lake are confined to 

 the deep waters, and that the change from the shallow to the deep 

 water fauna takes place at a depth of about 30 fcithoms, at which depth 

 the character of the bottom and the annual temperature both become 

 nearly uniform. The following table will present more clearly the dis- 

 tribution of the species in depth. Under the first column I have checked 

 those species which are really free-swimming animals, most frequently 

 found at the surface ; and under the second, those which live in very 

 shallow waters along the shores, &c. The table is of course very im- 

 l)erfect, even for those species which are included. Most of the species 

 • of Mollusca, which now appear only in the second column, undoubtedly 

 occur in 4 to 8 fathoms or deeper; but I have only checked iho, species 

 as far as they have actually been observed at the depths indicated. 



Cbironomiis, sp., a. 

 Chiroiioniiis, sp., b. 

 Chiionomus, sp., c. 



EphemerW w 



PhrygaueiilfD 



Hydrachna, sp 



CllUSTACEA. 



Cambanis, sovei'al species. 



]\[ysis relicta 



Hyalella deutata 



I'oiitoporeia Hoyi 



Gammarus limuwus 



Craiigonyx ptracilis 



Asellopsis tenax 



Uaphiiia galeata 



Dapluiia pellucida 



Daphnia pulex ? 



Bosmina, sp 



Eurycercus lanjellatus? 



Ijoptodora hyaliua 



Ostracoda 



Copepoda 



LernaBopoda siscowet 



Lernffiopoda ? Curegoni 



WORMS. 



Lumbricus laciistiis 



Srenuiis aV)y s.sicDla 



Saiiniris limicola 



Chirodrillus larviformis . 

 Chii'odrillus abyssorum. . 



Tiibifex profuiidioola 



Macrobdella decora 



Aulastnmum lacustre . . . 



■Seniiacolex grandis 



Kepbelis lateralis 



Kepbelis fervida 



Clepsiue papillifera 



lelithyobdt'lla punctata . , 

 Procotyla fluviatilis 



Surface. 



Shore. 



Depth in fathoms. 



4-8. 10-20. 30-50. 60-100. 100-1C9, 



x(?) 



x(?) 



x{?) 



x(?) 



X (Y)' 



x(?) 



