1868.] meeting of the american association. 303 



On the geographical distribution of the Radiates on 

 the West Coast of America ; by Prof. A. E. Verrill. — 

 Eleven distinct marine zoological provinces have been recognized 

 along the coast, each characterized by the existence or prevalence 

 of peculiar genera and species. These provinces were discussed 

 by Prof. Verrill, in detail, the characteristic species, and the 

 conditions under which they exist stated, the number of species of 

 each class of Radiates known to exist in the several provinces, and 

 number peculiar to the respective provinces given, and each Pacific 

 shore region compared with parallel regions on the Atlantic 

 coasts of America and Europe. Distribution is effected mainly 

 by temperature, less by the nature of the bottom and shore. 

 Depth of water exerts principally an indirect influence by 

 diminishing the temperature as we descend. A few Holothurians 

 are the only Radiates recorded as common to the Atlantic and 

 Pacific. The Polyps and corals of the two seas differ widely. 

 The mollusca, Crustacea, fishes, and echiuoderms are usually 

 specifically distinct, but the genera and families of these groups 

 are often identical. No direct evidence exists of a water commu- 

 nication across the Isthmus later than the cretaceous period. 

 Prof. Verrill concludes that all the phenomena observed in the 

 distribution of identical species may be accounted for by supposing 

 a former depression of about 300 feet, which would cause a 

 connection across the Isthmus by means of a shallow, brackish 

 estuary, capable of sustaining the life of many mollusca, Crustacea, 

 and fishes, but not the genera of corals and other Radiates. In 

 the case of distinct, but similar species, we must suppose different 

 centres of creation, or a descent from common ancestors, the 

 distribution having taken place at a very early period, when an 

 extensive connection existed between the two oceans. The animals 

 on the latter supposition have subsequently become distinct, by 

 natural selection, or otherwise. 



Considerations relating to the Climate of the 

 Glacial Epoch in North America ; by Prof. E. Hungerford. 

 — The object of this paper was to discuss the growth, and climatic 

 influence of such an accumulation of ice and snow as the glacial 

 hypothesis supposes to have once existed. The result of an 

 elevation of the northern part of the continent would be to lower 

 the snow line by depressing the mean summer temperature. If 

 the surface were raised by the accumulation of frozen snow, 

 instead of by an upheaval of the land, the frigorific effect would 



