CRUSTACEA MALACOSTRACA. III. 53 



Group IV. Schistosomatini. 



It was deemed unavoidable to establish this group on a single genus (with a single species), 

 which seems to be intermediate between other groups, and rather distant from them all. In order to 

 avoid reiterations no characterization of the group is given, as the description of the genus together 

 with the remarks mav be sufficient. 



Schistosoma n. gen. 



Description. Head somewhat similar to that of Dcsmosoma; no eyes. Antennulae moderately 

 long (PI. IV, fig. 4 a); the basal joint somewhat slender and very oblong. The four proximal joints of 

 the antennae moderately short, robust (the two distal, probably strong joints of the peduncle and the 

 flagellum lost); squama very small. — Mandibles (fig. 4d) somewhat slender, in the main as in the 

 /em/ra-group ; left mandible has the incisive margin somewhat long, a slender movable lobe and a few 

 setae; the molar process is vertical on the corpus mandibular slightly tapering towards the end, which 

 is cut off, with the end irregularly shaped and adorned with a few short setse; palp well developed. 

 - Maxillipeds (fig. 4 e) in the main as in /antra; second joint very broad; its lobe large, almost as 

 long as the joint itself, much longer than broad, with the terminal margin very oblique and showing 

 some triangular teeth; the palp has the first joint very broad, second joint moderately broad and longer 

 than broad, third joint only a little more than half as broad as the second and broader than long, the 

 two distal joints well developed; epipod somewhat small. 



Thorax (fig. 4 a) divided into two sections, because the fifth segment is narrowed in front as a 

 kind of short stalk. All segments movable. The three anterior segments laterally produced into oblong 

 protuberances directed outwards and forwards ; the fourth segment has two pairs of lateral protuberances, 

 the first pair directed somewhat forwards, the second pair somewhat backwards; the three posterior 

 segments each with a pair of lateral protuberances, projecting outwards on the fifth segment, a little 

 backwards on the sixth, and much backwards on the seventh segment. All these thoracic protuberances 

 have the terminal part moderately slender, the end cut off, and the coxae are inserted at the base of 

 the protuberances; the coxae have no processes. 



First pair of legs (figs. 4 a and 4 f) moderately short and very slender, scarcely prehensile, without 

 spines; fifth joint somewhat elongate; sixth joint not thicker than the fifth; seventh joint very oblong, 

 as long as the very slender claw; especially the terminal part of sixth joint with a number of long 

 hairs. The six other pairs of legs somewhat long, slender, subsimilar; fifth and sixth joints rather 

 long, with very few, nearly setiform, short spines; seventh joint (fig. 4 h) very oblong, terminating in 

 a somewhat slender claw and a seta. 



Abdomen (in the male) shows two segments; first segment is slender and somewhat long; the 

 second is oblong-ovate, twice as broad as the first. The male operculum occupies nearly the whole 

 lower surface of the main part of the abdomen; the median lamella tapers considerably from the base 

 to the end. — Uropods inserted on the lateral margins rather near the end; they are somewhat short, 

 uniramous, two-jointed. 



