8 CRUSTACEA MALACOSTRACA. II. 



D. Some morphological Features in Agathotanais n. gen. 



Among all the new species described in the present paper only one, viz. Agathotanais Ingolfi 

 n. gen., n. sp. shows hitherto unknown features of more general interest. Both females without mar- 

 supium and subadult males are at hand (PI. VI, figs. 5 a 50). In the female the antennae consist of a 

 single minute joint (fig. 5c); in subadult males this joint is considerably larger (fig. 5n). In all specimens 

 the seventh thoracic segment and all abdominal segments are immovably fused, but the limits between 

 the segments are tolerably indicated by fine furrows (figs. 5 b and 50). The pleopods are wanting in 

 the female (fig. 5b); in the subadult males they are rather long, unjointed, very slender conical and 

 all coalesced, constituting a kind of pyramid with longitudinal furrows between the pairs, and each 

 pleopod terminates in a few very short setae (fig. 50). The uropods are rudimentary, each being a 

 small, subtriangular joint without any distinct division (figs. 5! and 5111). 



Among these features the rudimentary state of antennae and uropods are mere reductions, 

 which yet are much stronger than in any other genus. The fusion of seventh thoracic segment and 

 all abdominal segments is still more interesting. But completely without parallel among Crustacea 

 is the fact, that in the subadult male all five pairs of pleopods are coalesced forming a single 

 somewhat long protuberance, and this fact is of importance for comparison with features found in 

 mouth-parts in a couple of groups of high rank of terrestrial Arthropoda. 



E. On the naming of Segments and Joints. 



Before entering on the systematic part it may be useful to say a little on the counting of the 

 segments and joints and the terms used in the descriptions. 



As the first thoracic segment is always fused with the head and hidden beneath the carapace, 

 the apparently first segment is in reality the second, consequently it is here named the second and 

 its legs the second pair, while the first pair of legs, the chelipeds, as belonging to the cephalothorax, 

 are described separately. 



The counting of the antennular joints presents no difficulty. But the antennae are less easy. 

 When the antennae of females are fully developed they contain seven joints, as is seen in many species 

 of Leptognathia. The first joint is very short, frequently nearly triangular, as the posterior margin is 

 oblique and the upper margin very short or wanting; this joint is sometimes difficult to perceive and 

 I never describe it, but it must of course be taken into consideration by counting. The two next 

 joints are somewhat short and the third as a rule shorter than the second; in a couple of species of 

 Typhlotanais these joints are strongly armed below. Fourth and fifth joints are somewhat long, but 

 frequently, as in Typhlotanais, in some species of Leptognathia, in Paranarthrura, etc., fused, constituting 

 a single long or very long joint sometimes with a vestige of division. Sixth joint is well developed, 

 seventh always very small. 



The thoracic legs have always the second joint long; the first joint is quite short but most 

 frequently discoverable. The "claw" on the sixth joint is composed of the seventh joint and the real claw, 

 and the limit or suture between these two parts is jnost frequently distinct. In the descriptions the 

 joints are named according to their real number. 



