88 CRUSTACEA MALACOSTRACA. III. 



male of A r . oblongus first pair of legs are very thickened and, besides, armed with a few very strong 

 spines, thus differing very much from the rather slender first pair in the females of N. oblongus ; 

 furthermore, not only the operculum but the outline of the body and the flagella of the antennae in 

 the specimen figured by Sars as the male show exclusively female features. Consequently I consider 

 the specimens described by Sars as being the males of N. oblongus to be in reality immature females 

 with protandrous features in the internal sexual organs of a species with the first pair of legs very- 

 thickened; I propose the name N. crassipes for this peculiar form. 



Until 1914 G. O. Sars was the only author who had published anything based on personal 

 observation on the genus Nannoniscus. In 1914 E. Vanhoffen established (in: Die Isopoden der Deut- 

 schen Siidpolar-Exped. 1901 1903) two new species from the Antarctic Ocean, but descriptions and 

 figures are rather poor. My material from the "Ingolf" area is extremely rich, comprising 13 species, 

 12 of which are new; of five species both males and females, of eight species only females, are to hand. 

 Sars' figures of the female of A', oblongus and of the male of N. caspius convey together an excellent 

 idea of the genus, but the rich material enables me to add some remarks to his description of the 

 genus, and to point out some sexual differences. 



The outline of the body differs somewhat in the two sexes. In the females at least the three 

 anterior thoracic segments are somewhat or considerably broader than the three posterior segments 

 and abdomen, while in the males the anterior segments are a little narrower, but the posterior seg- 

 ments and abdomen broader, than in the other sex, with the result that in the males the posterior 

 half of the body is almost or completely as broad as the anterior portion (PL VIII, fig. 33; PL IX, 

 fig. 2 a). The front area on the head is marked off laterally, and in most species by keels, each ter- 

 minating anteriorly in an acute angle; the anterior margin of the front area is straight, concave or 

 convex, and the length of this margin differs always in the sexes, being longer in the females than 

 in the males, and it affords excellent specific characters. 



The antennulse are extremely characteristic (many figures on Pis. VIII X), differing materially 

 from those in any other Isopod, but the representations published by Sars are not quite correct. They 

 are always rather short and consist of five joints. First joint is large, thick and more or less oblong; 

 second joint is more or less slender at the base and increases in thickness to the end, which is cut 

 off and, besides, produced in probably always three short protuberances or somewhat long processes; 

 third joint is extremely short and thin, and not unfrequently difficult to perceive, while the fourth 

 joint, which is short, is at the inner side of the end produced into a very conspicuous, oblong, oblique 

 process. Fifth joint is always a vesicle, ovate (for inst. figs. 2 d and 7 c on PL IX) or, rarely, very 

 oblong (PL IX, fig. 4 b), at least frequently with a couple of fine hairs on the distal part of the lower 

 side; it is attached to the end of fourth joint by an extremely narrow articulation. 



The antenna; have the squama distinct, sometimes quite small, in N. oblongus and especially 

 in A f . caspius long; it is most frequently, but not always (as in N. oblongus, PL VIII, fig. 4f) marked 

 off by a suture from third joint Fifth and sixth joints moderately long. The flagellum is slender 

 and normal in the females; while in the males a considerable part (PL VIII, fig. 6d) or almost the 

 whole flagellum (PL IX, fig. 6 a) is thickened, and in the thickened part the joints are fused and not 

 discernible. The mouth-parts have been well described by Sars. 



