November, 1920] 



The Canadian Field-Naturalist 



145 



Diadophis puctatus (Linne.) Ring-necked 

 inake. . . 



In the summer of 1913 we recorded six speci- 

 mens of this species, mainly along the road to Dor- 

 set and on the cliff to the west of camp. In 1919 

 one was found in mid- August between Otter lake 

 and Dorset. 



Liopeltis vernalis (Harlan.) Green Snake. 



Meek secured one at Gravenhurst and G. S. 

 Miller, Jr., Aug. 6, 1896, saw a green snake at 

 this same place. Several of the natives voluntarily 

 described a "grass green snake net very common. 

 We have not yet taken it. 



Nairix sipcdon sipedon (Linne.) Water Snake. 



Meek took one specimen at Gravenhurst and the 

 species is uncommon in the Lake of the Bays re* 

 gion. Many of the natives call it a "black snake." 



Sioreria occipiio-maculata (Storer.) Red- 



bellied Snake. 



This and the ring-necked snake are of about 

 equal occurrence in the region. Through 1913 

 and in August, 1919 we recorded four specimens 



of this species. 



Thainnophis sirtalis sirtalis (Linne.). Garter 

 Snake. 



Abundant ; the snake of the region. On August 

 11, 1913 one of our captive garters gave birth to 

 19 young. 



The Turtles. 



Chelydra serpentina (Linne.). Snapping Turtle. 



Uncommon. Found more in muddy creeks and 

 ponds than in the open lake. We took one July 

 23, 1913, in Fletcher lake with a carapace length 

 of 18-20 inches. On the road to Dorset in the 

 last of August, 1919, another specimen was taken 

 \7!lh head width of three inches. Sometimes called 

 "Black-turtle" in this region. 



Chrysem])s marginata marginala (Agassiz.) 

 Western Painted Turtle. 



We have not seen this form in this region but 

 the natives describe a small mud turtle other than 

 the snapper and the description accords well with 

 this species. 



(To be continued.) 



THE LARGER FRESHWATER-CRUSTACEA FROM CANADA AND ALASKA. 



By Frits Johansen. 



(Continued from Vol. XXXIV, page 132) 



II. ISOPODA. 



This order of Crustacea has a great number of as in the amphipods, and the young oncs also re- 

 representatives in the sea, some of which live para- main inside the pouch some time after hatching. The 

 sitically on fishes, other Crustacea, etc., and are newborn young are practically like their parents 

 correspondingly deformed, especially the females. though different in color and the proportional size 



of the various parts of the body, and the embryonal 

 development inside the egg is said to be not quite 

 so complete as with the amphipods. A popular 



Three families are known freni-freshwater on this 

 continent. 



They have the following characters in common 

 with the amphipods; a many segmented body, no 

 carapace, but the head and first thoracic segment 

 united, and the eyes, when present, sessile. While 

 the body of an amphipod is compressed that of an 

 isopcd is depressed thus making the latter a less 

 capable swimmer, but admirably suited for dodg- 

 ing under stones, etc., and attaching itself to moving 

 animals. It is true that certain of the marine forms 

 (Mesidothea sp.) are good swimmers (using their 

 legs), and live almost a pelagic life when they are 

 very young (just after leaving the brood-pouch), 

 but they soon -change this for crawling over or bur- 

 rowing in the sea bottom, the typical life for most 

 cf the isopods. The eggs are carried by the females 

 on the underside of the body in a brood-pouch,* 



*Formecl by lamellae from the thoracic legs. 



name for the isopods is "sow-bugs," and it is well 

 known that certain of them (Oniscus, etc.) live on 

 land under bark or stones, etc. The marine and 

 terrestrial forms are predacious, while those in 

 freshwater feed upon decaying vegetable matter. 

 Owing to their more hidden habit the freshwater 

 forms are not quite so important an item in the 

 food of fishes, birds, etc., though the marine or 

 brackish water forms are decidedly so. Among the 

 latter is the large interesting species Mesidothea 

 entomon, which has a circumpolar distribution and 

 also is found as a glacial marine relict in the large 

 lakes cf Sweden and in the Baltic. In the arctic it 

 is a littoral form and one cf the most characteristic 

 and commonest invertebrates along the coast west 

 of Hudson Bay. I have observed (arctic Alaska") 

 how it will enter the estuaries of rivers or smaller 

 water courses at hieh tide, remain there in quie* 



