Freshwater Copepoda TJ 



is shown in PL III, fig. 5. Schmeil, 1893, has shown that there may be much 

 variation in the length of this appendage. 



The male fifth foot is shown in PI. Ill, fig. 4. The second basal segment of 

 the right foot has the small lateral seta near the distal end of the segment; from 

 about midway of the inner border projects a hyaline lamella, which extends 

 over the central third of the segment. The first segment of the right exopodite 

 is sharply produced at its outer distal angle. The second segment is not quite 

 twice as long as its greatest width. The lateral spine is straight, acute, nearly 

 as long as the segment, and placed just beyond the middle. The terminal hook 

 is sickle-shaped and slender. Some authors say that there is a projection or 

 spine on the dorsal surface of the second segment of the exopodite; this is shown 

 by Kolbel, but not by Sars, 1903. Schmeil, 1893, says that it is variable, being 

 sometimes present and sometimes absent.. The second basal segment of the left 

 fifth foot of the male has the small lateral hair well towards the end of the segment. 

 At about the middle of the inner border is a small hyaline lamella, and from the 

 inner distal angle extends distally a cuticular, tooth-like projection. The 

 terminal segment of the left foot has a digitiform process and a curved spine. 

 The endopodites are indistinctly two-segmented. Kolbel and Sars, 1903, say 

 that the endopodites are one-segmented, but DeGuerne and Richard, 1889, in 

 their figure, make them indistinctly two-segmented. DeGuerne and Richard 

 state that the left endopodite of the male fifth foot is not separated by a joint, 

 and the figure of Sars, 1903, shows the same condition. Kolbel, however, figures 

 a joint, as does Sars, 1898. 



It is in the structure of the second basal segments of the male fifth feet 

 that we find the characteristics which are most diagnostic of this species of 

 Diaptomus. They were not figured fully by Kolbel, but they appear in the later 

 authors with a rather surprising lack of variability. This lack of variability is 

 the more surprising because of the marked resemblance in the general structure 

 of the male fifth feet in D. bacillifer Kolbel, D. laticeps Sars, D. salinus Daday, 

 D. acutilobatus Sars, D. wierzejskii Richard, D. hircus Brady, and D. similis 

 Baird, as defined by Richard. 



D. bacillifer has been found in Scotland, Norway, many places in the Alps, 

 Asia Minor, Syria, the Caucasus, India, Central Asia, Siberia, and in islands 

 north of Siberia. It is a stenothermal cold-water form, and is found in the far 

 north in bodies of water near the sea level, and farther south in lakes in the 

 higher mountains. 



In the collections of the Canadian Arctic Expedition it was found only in 

 the gathering made on October 6, 1915, from a pond one foot deep a hundred 

 feet above sea level on a ridge at Bernard harbour. Some Diaptomi collected 

 on St. Paul island, Alaska, by Professor Parker, were sent to the author some 

 time ago, and proved to be of this species. Apparently then, it encircles the 

 world in the general neighbourhood of the Arctic circle, and probably will be 

 found in many of the bodies of water in northern Canada. It seems strange 

 that it has not appeared in the collections which have been made in Iceland and 

 Greenland. 



D. bacillifer has the distinction of having a wider distribution than any other 

 species of the genus. 



Diaptomus arcticus, n. sp. 



Plate III, figs. 6-9 and 13. 



This large and conspicuous species is closely related to D. shoshone, so closely 

 in fact, that it can only be distinguished from that species by details of the 

 structure of the abdomen and fifth feet. 



The first abdominal segment of the female is dilated laterally and in front 

 and bears on either side a blunt spine. This is shown from the side in PI. Ill, 

 fig. 6. The antennae equal in length the cephalothorax. In the fifth foot, 



