32 



CRUSTACEA MALACOSTRACA. III. 



The articulation between fifth and sixth thoracic segments seems to be not quite undeveloped, 

 while the two posterior segments and the abdomen seem to be immovably coalesced, and the limits 

 between them are on the major part of the upper surface only moderately distinct sutures, but con- 

 spicuous towards the lateral margins. On the thoracic legs the claw is longer than the seventh joint (fig. 4 c). 



Abdomen more than half as broad again as long (figs. 4 a and 4d); the postero-lateral processes 

 are small, broader than long, acute; the posterior margin is more convex than in the two preceding 

 species. — The operculum is nearly circular. — The uropods are very small, not reaching the end of 

 the processes; a division into two joints could not be observed. 



I y ength of the largest specimen, a female without marsupium, 1-5 mm.; the other specimen juvenile. 



Remarks. In general aspect H. armadilloides differs considerably from the two preceding 

 species, and it can roll itself nearly as many terrestrial Oniscidse. It agrees with H bicuspis in several 

 features, thus in having a peculiar process on third antennal joint, in the postero-lateral abdominal 

 processes, the shape of the uropods, the abdominal operculum, but shows a number of sharp differences, 

 which, at least provisionally, are considered as not being of generic value. 



Occurrense. Taken by the "Ingolf" at a single station. 



South of Iceland: Stat. 54: Lat. 63°o8' N., L,ong. i5°4o'W., 691 fath., temp. 3-9°; 2 spec. 



Hydroniscus n. gen. 



Description. Of this curious genus only the female is known, and it is related to Haploniscus. 

 - Body oblong, highly vaulted and contractile into globular form. Head anteriorly with a broad, 

 rounded incision at each side of the moderately broad median part, which is produced as an obtuse 

 process (PI. II, fig. 5 c). — Antennulse moderately short; second joint longer than in Haploniscus. 

 Antennae short; third joint without process. — Mandibles (figs. 5 d— 5 e) somewhat similar to Ianira, 

 but the molar process is more thickened towards the end, and the movable lobe is very strong on the 

 left mandible. Maxillipeds (fig. 5 f) with the two proximal joints and the epipod somewhat broader 

 than in Haploniscus, while second and third joints of the palp are still more slender than in that genus. 



The three posterior thoracic segments and the abdomen are strongly vaulted (fig. 5 b) and, 

 besides, so completely fused that only two rudiments of articulations between segments are visible on 

 the sides; seen from above the abdomen has the lateral margins somewhat convex and converging to 

 the narrowly rounded end (fig. 5 a); seen from the side (fig. 5 b), the lateral margin terminates in a 

 small, triangular tooth not visible from above, and situated in advance of the somewhat protruding 

 end of abdomen. — Thoracic legs slender, especially the posterior pairs; first pair (figs. 5 g and 5 h) 

 with seventh joint moderately long and rather slender, on the posterior pairs (fig. 5 i) long and very 

 slender; the claw rather long, shorter than seventh joint, and an accessory claw is wanting. 



Operculum (fig. 5 k, 0) subangular before the middle. — Uropods completely wanting. 



Remarks. It is easily seen that this genus is closely related to Haploniscus in spite of its 

 peculiar aspect. It was impossible to find any vestige of uropods; if lost, their points of attachment 

 must be discoverable. 



Only a single species is known. 



