SYSTEMATIC REPORT 155 



kidney-shaped and laterally directed; pigment black (Fig. 36 A). Mandibles with no spine or acute 

 point at the outer distal angle of the second segment of the mandibular palp. Thoracic appendages. The 

 endopods of the third to the eighth thoracic appendages are not unusually long in the female, but be- 

 come progressively longer from the third to the seventh pairs. That of the eighth pair is a little shorter 

 than the seventh. The carpo-propodus is composed of 9-10 sub-segments (Fig. 36 G). In the male the 

 thoracic endopods are larger than in the female and the seventh pair is very much enlarged, especially 

 the carpo-propodus. This is composed in adult males of twelve sub-segments, which are very swollen 

 and profusely armed with long setae. The distal portion of the outer margin of the merus is armed with 

 7-8 extremely long setae (Fig. 36 E). The eighth thoracic endopods are much smaller than the seventh; 

 the ischium is somewhat swollen distally, the merus has no long setae and the carpo-propodus is 

 small and curved so that it looks deformed. I have found this peculiar curvature in all the males 

 I have examined (Fig. 36 F, G). Genital appendage slender, extending forward as far as the second 

 thoracic somite. Uropods small; endopod only slightly longer than the telson; inner margin armed 

 with about twenty spines from the distal end of the statocyst to within one-third of the distance from 

 the apex; the proximal five spines of the row are very small (Fig. 36 H). Telson small, middle region 

 of the lateral margins convex; lateral margins armed throughout with a close row of spines, which 

 are relatively rather large and only in the middle region of the margins show a tendency to arrange- 

 ment in series of larger spines with smaller ones in the spaces between them; cleft widely open and 

 shallow, armed with about twenty teeth on each margin (Fig. 36J). 



Length of largest male which appears to be adult, 13-6 mm.; adult female, 14 mm. 



Remarks. It is very easy to recognize adult males of this species by the enlarged seventh thoracic 

 endopods with swollen, hirsute sub-segments of the carpo-propodus and by the small, distorted-looking 

 distal end of the eighth thoracic endopods. Young males and all females can be distinguished by the 

 very short rostral plate, by the armature of the third segment of the antennular peduncle, by the 

 widely spaced eyes with their black pigment, by the small, slender antennal scale, by the small uropods 

 and by the shape and armature of the telson with its open, somewhat shallow cleft. The differences 

 shown by the males are so marked, that at first I thought that they represented another species, but 

 in young immature males the antennular peduncle does not differ markedly from that of the female 

 and the endopods of the seventh and eighth thoracic appendages are not so much modified, although 

 even in quite small males, the eighth are much smaller than the seventh. The material from several of 

 the stations is in bad condition and I only tentatively refer the damaged specimens from station 190 

 to M. dimorpha. 



Distribution. All the stations at which M. dimorpha was taken are situated around South Georgia, 

 most of them from East Cumberland Bay, with the exception of the very doubtful record from station 

 190 in the Palmer Archipelago. Numerous immature specimens were taken in water of 18-40 m., 

 but only a few specimens and fragments occurred in depths of over 100 m. 



Genus Mysidopsis G. O. Sars, 1864 



1864 Mysidopsis G. O. Sars, p. 249. 

 1912 Paramysidopsis Zimmer, p. 4. 

 1918 Mysidopsis, Zimmer, p. 17. 



Remarks. This genus is characterized by the presence of only six segments in the endopod of the 

 first thoracic appendage, due to the fusion of the third and fourth segments. The telson is variable. In 

 most of the species it is short and linguiform, with the lateral margins markedly convex near the base 

 and narrowing slightly to a broadly rounded or narrowly truncate apex. In one or two species there 



