280 Canadian Record of Science. 



capable of transmission for great distances. In considering 

 this, we cannot fail to conclude that the union of simple 

 cryptogamous fructification with arboreal stems of high 

 complexity, so well illustrated by Dr. "Williamson, had a 

 direct relation to the necessity for a rapid and wide distri- 

 bution of these ancient trees. It seems also certain that 

 some spores, as, for example, those of the Ehizocarps, 1 a type 

 of vegetation abundant in the Palseozoic, and certain kinds of 

 seeds, as those named JEtheotesta and Pachytheca, were fitted 

 for flotation. Farther, the periods of Arctic warmth per- 

 mitted the passage around the northern belt of many tem- 

 perate species of plants, just as now happens with the Arctic 

 flora ; and when these were displaced by colder periods, they 

 marched southward along both sides of the sea on the 

 mountain chains. 



The same remark applies to northern forms of marine 

 invertebrates, which are much more widely distributed in 

 longitude than those further south. The late Mr. Grwyn 

 Jeffreys, in one of his latest communications to this Asso- 

 ciation, stated that 54 per cent, of the shallow-water mol- 

 lusks of New England and Canada are also European, and 

 of the deep-sea forms 30 out of 35 ; these last, of course, 

 enjoying greater facilities for migration than those which 

 have to travel slowly along the shallows of the coast in 

 order to cross the ocean and settle themselves on both 

 sides. Many of these animals, like the common mussel and 

 sand clam, are old settlers which came over in the Pleisto- 

 tene period, or even earlier. Others, like the common 

 periwinkle, seem to have been slowly extending themselves 

 in modern times, perhaps even by the agency of man. The 

 older immigrants may possibly have taken advantage of 

 lines of coast now submerged, or of warm periods, when 

 they could creep around the Arctic shores. Mr. Herbert 

 Carpenter and other naturalists employed on the Challenger 

 collections have made similar statements respecting other 

 marine invertebrates, as, for instance, the Echinoderms, of 

 which the deep-sea crinoids present many common species, 



1 See paper by the author on PalreozoicRhizocarps, Chicago Trans. 

 1886. 



