The Fresh Water Copepoda of the Canadian Arctic Expedition 



1913-18 



By C. DWIGHT MARSH 



U. S. Department of Agriculture 



The collections of the Canadian Arctic Expedition were of especial interest 

 from the standpoint of geographical distribution, as the localities included a 

 region from which no previous collections had been made. Copepoda have 

 been collected in Iceland, Greenland, Newfoundland, Alaska, and lakes in the 

 province of Saskatchewan, but the region north of Saskatchewan is practically 

 unexplored, so far as entomostraca are concerned. If it is assumed, as is generally 

 done, that with the retreat of the ice of the glacial period, there was a migration 

 towards the north of the species adapted to the conditions of cold water, we should 

 expect to find, so far as North America is concerned, the more primitive forms 

 in the arctic or sub-arctic regions. These forms might continue further south 

 as a fauna relicta, where altitude made a suitable environment, but where 

 climatic conditions were radically changed, changes in structure would occur 

 which might result in the formation of new species. That this has actually 

 occurred in North America is very probable, as has been indicated in Marsh, 

 1907, pp. 384 and following. Therefore collections from an unexplored region 

 of the northern part of the continent are of particular interest, and it is to be 

 hoped that further collections can be made both in the Arctic and in the region 

 immediately south, of which practically nothing is known. 



All the specimens were collected by Mr. Frits Johansen, naturalist on the 

 expedition, in various lagoons, ponds, and lakes along the Arctic coast; es- 

 especially at the two winter headquarters of the expedition, Camden bay, Alaska, 

 and Dolphin and Union strait, Canada. At the other places only shorter visits 

 were made in the summer time. 



Genus Limnocalanus. 

 Limnocalanus johanseni, n. sp. 

 Plate I, Figs. 1-8. 



The first segment of the cephalothorax is nearly one-half the length of the 

 cephalo thorax. The front is armed with two projections. The last cephalo- 

 thoracic segment is rounded on the sides and each side is armed with a small 

 spine, which may be sharp, as in PI. I, fig. 1, or blunted, as in PL I, fig. 2. 



The abdomen of the female, PL I, fig. 3, consists of three segments: the 

 first segment is somewhat expanded laterally and is about twice as long as the 

 second; the third segment is slightly longer than the second. The branches of 

 the furca are three times as long as wide and are about half again as long as the 

 third segment; they are ciliated on their internal margins, and have the typical 

 armature of setae. 



The male abdomen, PL I, fig. 4, consists of five segments, of which the first 

 three are about equal in length; the fourth and fifth are somewhat shorter 

 and about equal to each other. The length of the furcal branches is about 

 three and one-half times the breadth, and about equals the two preceding 

 segments. The furcse are ciliated on the internal margins. 



The antennae of the female when reflexed reach the second abdominal seg- 

 ment. The cephalothoracic appendages of the female are like those of L. 



