NO. 5.] ACCOUNT OF THE SPECIES. 47 



side, and one rather large, and finely denticulated spine inside. Length of 

 adult female scarcely exceeding 2 mm. 



Remarks. As stated above, this form is very different from the type 

 species, S. Dance, Lubb., and more closely resembles the 2nd species recorded 

 by Brady, minor; but also from this species, it may easily be distinguished 

 by the comparatively shorter anterior antennae, and the more regularly rounded 

 frontal part. It is somewhat more difficult to point out the distinguishing 

 characters in relation to the other species established by Dr. Giesbrecht. I 

 believe, however, that the polar form is specifically distinct from any of them. 



Description of the Female. 



The length of fully adult specimens does not exceed 2 mm. 



The general form of the body (see figs. 1 & 2) is rather short and thick, 

 as is also the case with the other species referred to this genus. The 

 anterior division, when seen dorsally (fig. 1), is rather regularly oblong oval in 

 form, with the greatest width behind the middle, and somewhat exceeding Vs 

 of the length. It gradually tapers both in front and behind, the anterior 

 extremity being evenly rounded, the posterior deeply incised in the middle. 

 The cephalic segment is quite coalesced with the 1st pedigerous one, both 

 together forming a very large segment, fully twice as long as all the others 

 combined. Seen laterally (fig. 2), this segment appears narrowly rounded in 

 front, whereas in S. minor it is almost transversally truncated. The rostral 

 projection (see also fig. 3) is well marked, and carries 2 slender tentacular 

 filaments. The last segment is imperfectly defined from the penultimate one, 

 and has its lateral parts obtusely produced behind on each side of the deep 

 median emargination (see fig. 1). 



The tail is rather small, scarcely exceeding in length Vs of the anterior 

 division, and it is narrow cylindric in form. Of the 4 segments composing 

 it, the 1st, or genital segment is, as usual, the largest, though shorter than 

 the 2 succeeding ones combined. The last segment is somewhat smaller than 

 the penultimate one. The caudal rami are about twice as long as they are 

 broad, and not at all divergent. The caudal setae in all the specimens found 

 were broken off, and their relative length cannot therefore be indicated. 



The anterior antennae (fig. 4) are comparatively short, not nearly attaining 

 the length of the anterior division of the body, and they are composed of only 



