NO. 1876. ON THE CRUSTACEAN ORDER CUMACEA—CALMAN. 607 



to point to the existence of an Arctic- American (but not circumpolar) 

 fauna, extending into the boreal regions on both sides of the Ameri- 

 can continent. I learn from Dr. W. H. Dall that there is some 

 evidence pointing in the same direction to be obtained from the 

 Mollusca, among which, however, there are some species common 

 to the east and west boreal regions that are not known from the 

 Arctic seas. 



As regards the relation between the faunas of the American and 

 European coasts of the Atlantic, the list given above includes a 

 considerable number of species that are common to both. The great 

 majority of these are species that range into the Arctic region and 

 have a continuous distribution in the colder waters of the north. 

 A few, like Cyclaspis longicaudata and Paralamprops orbicularis, are 

 deep-water species, for which we may suppose a similar continuity 

 in the deeper levels. There remain a small number of forms, of which 

 Eudorella truncatula is an example, wliich are neither truly Arctic nor 

 deep-water species. These appear to exist in separate colonies on the 

 two sides of the Atlantic, and, as in the similar case of the European 

 and American lobsters (Homarus gammarus and H. americanus), we 

 should expect to find at least the beginnings of specific differentiation 

 between the forms inhabiting the two areas. In the case of E. trun- 

 catula I have discussed the relation of the American form described 

 by Sars as E. pusilla to the European species, and, failing to find any 

 trustworthy characters on which to separate them, I have united 

 them under one specific name. It is by no means unlikely, however, 

 that some future student may be more successful in distinguishing 

 the two forms, which wUl then appear as representative species on 

 the two sides of the Atlantic, bearing to each other the same relation 

 that Lamprops quadriplicata bears to L. fasciata, or Diastylis quad- 

 rispinosa to D. cornuta. 



In aU these cases, however, we need more evidence as to the range 

 of variation within the species, and there is abundant work stUl to 

 be done in comparing minutely and carefuUy the specimens from 

 various localities. 



Another element in the Cumacean fauna of the Atlantic coast of 

 North America is represented by Leptocuma minor and Oxyurostylis 

 smiihi. These appear to be southern types which reach their northern 

 limit on the New England coast. 0. smitJii is recorded also from the 

 Gulf of Mexico, while the only other species of the genus Leptocuma 

 occurs on the east coast of South America. 



Finally, there are a few species peculiar, so far as is yet known, to 

 the New England coast and adjacent waters and not obviously 

 related to species occurring elsewhere. To this group belong Dias- 

 tylis sculpta and D. polita. 



