192 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28 



The totals in the above table show that 48.6 percent of the animals 

 collected at Point Barrow are common to three oceans and 41.7 per- 

 cent are common to two — 19.3 percent to the Arctic and Atlantic, 

 22.4 percent to the Arctic and Pacific; while 9.6 percent have been 

 found in the Arctic only (two of the species also found in the Ant- 

 arctic). These figures bring out some facts that stimulate one's curi- 

 osity to say the least. Why have animals that have found their way 

 into one ocean below the Arctic not found their way into the other? 

 From what has been said under "Distribution," there must be factors 

 other than the rate of distribution that account for the range of these 

 animals. Temperature may be one of them but its limited variation 

 in the Arctic-Pacific should make it possible for any animal that 

 lives in the Arctic-Atlantic to extend its range into the Pacific. Per- 

 haps the constant flow of water from the Pacific into the Arctic may 

 be an important factor but if so, any animal found in the Arctic-Pacific 

 should also be found in the Atlantic. Such speculation could go on 

 endlessly, but it is of little value unless followed by the actual test- 

 ing of theories. 



From table 11, some interesting comparisons can be made be- 

 tween the individual groups: 85.0 percent of the annelids are found 

 in both adjacent oceans, while only 60.6 percent of the pelecypods 

 and 37.1 percent of the gastropod prosobranchs are found in both the 

 Atlantic and Pacific. More mollusks are common to the Arctic and 

 Pacific than to the Arctic and Atlantic. (This discrepancy may dis- 

 appear when the remaining 10 or 15 gastropods, which are either new 

 or else Atlantic forms, are identified, for they certainly are not 

 Pacific forms.) Of the amphipods 31.0 percent are common to the 

 Arctic and Atlantic while only 7.0 percent are common to the Arctic 

 and Pacific, and 25.0 percent are restricted to the Arctic. Two and 

 a half times as many nemerteans are common to the Arctic and 

 Pacific as to the Arctic and Atlantic. 



In general, it would seem that there should be more species com- 

 mon to the Arctic and the Atlantic because of the greater variation in 

 ecological factors on the Atlantic side. However, the totals show that 

 19.3 percent of the species are common to the Arctic and Atlantic as 

 against 22.4 percent common to the Arctic and Pacific. 



The large number of annelids that range outside the Arctic is in- 

 teresting and, because of the thorough study of this group by Dr. Pet- 

 tibone, the figures must be so accurate that it is safe to assume there 

 will be little change in them as future work goes on. Annelids would 

 seem to be more adaptable to varied conditions than are other marine 

 invertebrates, especially such groups as the brachiopods. 



