125 



dactylus styliform. Female operculum rounded, without any longitudinal keel ; 

 male operculum transformed in the usual manner. Uropoda not very large, simple, 

 Inarticulate, distal joint much larger than the proximal one. 



Remarks. — This genus was established by the present author as early as 

 in the year 1863, and was at that time included within the group "Isopoda remi- 

 gantia", answering to the now generally accepted family Munnopsidce. The reason 

 for this was that the 3 posterior pairs of legs were proved to act as pulling 

 implements, by which the animal is enabled to move freely through the water in 

 a backward direction. In their structure, however, these legs differ rather pro- 

 minently from those in the true Munnopsidce, and in most other characters this 

 genus resembles much more closely the 3 preceding genera, and may therefore 

 more properly be associated with them in a separate family. In the restriction 

 here adopted, the genus comprises as yet only 3 species, 2 of which will be de- 

 scribed below, the 3rd having recently been recorded by M. Jules Bonnier from 

 the Bay of Biscay under the name of D. elonyatum. 



1. Desmosoma lineare, G-. 0. Sars. 



(PL LIII, H. LIV, fig. 1.) 



Desmosoma lineare, G. 0. Sars, Om en anomal Gruppe af Isopoder. Chr. Vid. Selsk. Forhandl. 



1863, p. 11. 



Specific Characters. — Pody slender, linear in form, being in female almost 

 5 times as long as it is broad, in male somewhat shorter. Cephalon of moderate 

 size, irregularly rounded, frontal part somewhat produced, and transversely trun- 

 cated in female, slightly insinuated in male. The 4 anterior segments of mesosome 

 differing but little in shape, lateral parts in all of them curving anteriorly, and 

 terminating in an acute corner, which in male is produced to a strong spiniform 

 projection. Posterior section of mesosome exceeding in length the preceding part 

 of the body, and fully as broad, in male even somewhat broader, 1st segment 

 large and expanded, with the antero-lateral corners acutely produced. Caudal 

 segment in female semi-oval, in male broader, almost semicircular, edges evenly 

 curved. Superior antennae 6-articulate, 2nd joint the longest. Inferior antennae 

 in female scarcely longer than the anterior division of the body, last joint of the 

 peduncle longer than the penultimate one, flagellum about the length of those 

 joints combined, and composed of 12 — 14 articulations. Inferior antennse in male 

 considerably larger, attaining half the length of the body, 2nd joint of the pe- 

 duncle armed outside with a strong spine, the 2 outer joints considerably tume- 

 fied, and each having 2 spines at the end outside, flagellum pronouncedly fusi-^ 



