TROPIDOLEPTUS CARINATUS IN CHEMUNG FAUNA 357 



the adult oyster could live in it, it could not reproduce itself, for the larvae 

 would perish. But as the Gulf water flows over the sand-bars and shoals 

 alluded to, it becomes heated up by the summer sun, and reaches a tempera- 

 ture which permits, in favorable years at least, of successful spawning. Oysters 

 are accordingly confined to such places on the coast of Canada as present 

 conditions similar to those mentioned above. They exist in the Baie de 

 Chaleur, in some of the shallower inlets on the New Brunswick coast, at a few 

 points on both shores of Prince Edward Island, and on the Northern Coast 

 of Nova Scotia. In every case, however, we have to do with isolated colonies 

 inhabiting warm spots surrounded by a great belt of cold water, so that al- 

 though the larvae could be carried to great distances in the fortnight of their 

 free-swimming life, they are all killed off by the cold. 1 



Protecting bars may at times have been a factor in modifying 

 the temperature of the Devonian sea where Portage and Chemung 

 colonies of T. carinatus gained a foothold, as they are now in shelter- 

 ing the oyster at Prince Edward Island. But there can be no doubt 

 that all times during the upper Devonian the eastern or coastwise 

 belt of the Appalachian gulf was shallower than its more pelagic 

 portion. Its waters must also have been comparatively warm, 

 at least during the' spawning season of its molluscan fauna. Since 

 Tropidoleptus carinatus is confined in the late Devonian to the 

 sediments of this belt of comparatively shallow sea, and conse- 

 quently warmer water, we must conclude that its restriction 

 and late survival here was due primarily to the higher average 

 temperature of this part of the Devonian sea. 



X E. W. MacBride, "The Canadian Oyster," Canadian Rec. of Set., IX (1905), 

 154-55- 



