28 G Canadian Arctic Expedition, 1913-1918 



somewhat square in shape, and convex in front, in the middle of which the fairly- 

 large nauplius-eye is seen, and with the adjesive organ occupying almost the 

 centre of the dorsal surface of the head. The composite paired eyes are large, 

 with movable, more slender penduncles and of the usual, iridescent, blackish 

 colour. Their length is about that of the first pair of antennae situated next to 

 them. The second antennae are developed as large sickle-shaped claspers, 

 reminding one strongly of the mandibles of certain insect-larvae (Dytiscidae). 

 Their bases are confluent, uniting into the labium (see below) and more slender 

 than at the level of the composite eyes, where the basal joint is enormously 

 swollen (to give room for the powerful muscles) and ends inwardly in a broad 

 and flat part, somewhat triangular in shape and ending in a blunt point, well 

 shown in the dorsal view. The terminal joint of the claspers resembles a broad 

 and flat flsh hook, running out into a blunt and slightly curved terminus, and 

 with a widening occupied by two hooks a little more than half way down. Each 

 clasper is roughly spinose on the whole of the terminal joint, except for the 

 proximal half of the central thickest part. At the base of the terminal joint of 

 each clasper is a small hooked spine, on the inner side. The head is without 

 frontal process unless a small, heart-shaped appendix, made up of two halves, 

 situated between the bases of the two claspers, ventrally, can be considered as 

 such 1 (flg. 5c). The labrum is broadly spatulate, rounded at its free posterior 

 end. Behind it are seen the mandibles and two pairs of maxillae. The two 

 first abdominal segments of both sexes are fused together and much swollen, 

 owing to the development of the genitalia. The ventrally protruding part of 

 the latter has in the male somewhat the shape of the "sac" of the Cirriped, 

 Sacculina, parasitic upon the tail of crabs. With the fairy-shrimp this "sac" is 

 somewhat slender at its base, and occupied by the two coiled penes, their swollen 

 bases showing a granulated spiny chitinous and yellow surface (fig. 5d) . The free 

 ends of the two penes each form a coil somewhat resembling a snail-shell with a few 

 loose turns ; the spine in which each one ends (see A . bungei) is apparentlj' only pro- 

 truded occasionally, in the actual moment of copulation. The length of the 

 abdomen is a little less than that of the body (excluding the head), and has no 

 dorsal processes above the genitalia. 



The females (see text fig. 6) are a little larger (8-11 mm.) than the males, 

 mainly caused by an elongation of the abdomen. The head (fig. 6a, c) is more 

 rounded oblong than in the male, and of course smaller, owing to the little 

 deveopment of the second pair of antennae. The first pair of antennae seems 

 comparatively shorter than in the male, while the second pair is only a little 

 longer than the composite ej-es, and of the shape usual with female fairy-shrimps. 

 The nauplius-eye, adhesive organ and mouth parts ^ are of course as with the 

 male, as also the body with its foliaceous legs. The first and the last pairs of 

 the latter are shown in fig. 56 and d. They are similar to those of A. bungei 

 (Daday de Dees, 1910, fig. 17). 



In the female A. stefanssoni the last body segment and the two succeeding 

 abdominal segments are each produced laterally (fig. Qb) into a flap-process (import- 

 ant for copulation-purpose), very similar to the two similar ones found on the same 

 part of the b ody in the female Eubranchipus gelidus (Hay). They are, however, 

 not lanceolate-triangular as in E. gelidus, but more spoon-shaped. The ovisac 

 (fig. Qd) is very large and oval, its transversal diameter being longer than the 

 longitudinal. On its ventral side are seen two broad folds in the wall of the 

 ovisac probably supporting the latter in its movements. These females, secured 

 on October 6, 1915, had a great number of ripe, red-brown eggs filling the whole 

 middle part of the ovisac, the unripe part of the ovarium showing up as two 

 smaller masses above the ripe egggs. The abdomen is about the same length 

 as the body, owing to the great development of the ovisac. 



' It is probably a remnant of the "kidney-labrum," so largely developed in the nauplius and metan- 

 auplius stages of fairy-shrimps (see p. 17). 



'' There seems to be no "appendix" to the labrum ("kidney remnant") as with the male; that the 

 latter has it is the only case among fairy-shrimps 1 know of. 



