20 K Canadian Arctic Expedition, 1913-18 



responding tuberosity on the right Bl; when the left B2 is disarticulated and 

 viewed from the side, the lobe appears as the proximal end of an elevated border 

 (Fig. 23). On the anterior surface of the terminal joint of the left foot there 

 is an elongate depression beset with groups of very fine hairs, with a small se 

 beside it (Fig. 24). 



The mandible has five teeth followed by a group of small setae; the first 

 (ventral) tooth is large. The rostral eye has no lens. 



15. Acartia clausi Giesbrecht. 



Station 17 (Table XI), station 18 (Table I), station 20a (Table IX), station 



21 (Table II), station 25 (Table III). Station 20^1: Port Clarence bay, Alaska, 

 water depth three fathoms, net number 3, surface-tow five minutes, amongst 

 seaweed, August 4, 1913. A small vial contained a number of Cladocera (Podon 

 leuckarti and Evadne nordmanni), a young Caprella, and several Acartia clausi, 

 male and female. The arrangement of the setae on the swimming legs agrees 

 with the description given by Giesbrecht, and the first basal joint (Bl) of the 

 second to the fourth feet has an emarginate outer border and an incised inner 

 border as in the type. 



Station 25, off Cooper Island, near Point Barrow, is the only station within 

 the Arctic Circle where this species was taken, although station 21 lies north 

 of Bering strait. Port Clarence lies to the south of the strait, about 65*^ 

 north latitude. Sars (1903) has never met with A. clausi in any samples of 

 plankton from the Arctic Ocean. On the south and west coasts of Norway 

 it is as common as A. longiremis with which it is often found. 



This species is more of an estuarine and inshore form than is A. longiremis. 



16. Acartia longiremis (Lilljeborg, 1853). 



This is an Arctic species with a wide southern extension. 



Station 66. 56° 26'N., 133° OO'W., just below the surface, 15 minutes, net 

 No. 4, June 24, 1913. This was a thin Acartia plankton, numbers of A. longire- 

 mis being noted and, in addition, two male Cumaceans and several Ostracods. 



Station 126, c. 54° 38'N., 157° 45'W., two surface tows of five minutes 

 each, net number 3, June 30, 1913. A few A. longiremis cf and 9 were taken, 

 together with a trace of Oithona and a number of young Amphipoda-Hyperidea. 



Station 13 a, 6, c. 54° 30'N., 159° 42'W., three surface tows of five minutes 

 each, net number 3, July 1, 1913. The catch was very scanty but there was a 

 male longiremis, 1-12 mm. in length; the number of setae on the inner border 

 of the two-jointed inner branch of the fourth foot (p. 4 Ri Si) is 3, 5, the same 

 as in A. clausi; Sars figures 2, 5. 



Station 17 a, 6, c. Table XL Whereas most Calanoids are largely dif- 

 ferentiated by male characters, Acartia is an exception, and the males of A. 

 clausi and longiremis are hard to distinguish, if the thorns are lost from the 

 last thoracic segment. 



Station 18: See under Calanus finmarchicus and remarks on table I. 



Station 19 a-e. 63° 43'N., 165° 24'W., surface, July 8, 1913, net number 



3, five tows of fifteen minutes each. Nearly fifty Acartia identified in part 

 as longiremis, about half as many young Paralabidocera, and a single male 

 Eurytemora herdmani. 



Station 21 a, 6, c, and d, e, f. Tables II and XII. 



Station 25 6, c. Table III. 



Station 36. Off cape Lyon, Darnley bay. Northwest Territories, net number 



4, surface tow of five minutes, August 23, 1914. Five males in company with 

 Eurytemora herdmani (q. v.). Phytoplankton was represented by Ceratium, 

 Chaetoceras and Coscinodiscus. 



