io 6 CRUSTACEA MALACOSTRACA. III. 



from the following pairs, and frequently strongly prehensile; the three following pairs of moderate 

 length, adapted for walking and more or less fossorial, especially second pair. The three posterior 

 pairs without epimera, decreasing conspicuously in length from fourth to seventh pair, and fourth pair 

 longer than any other pair ; these three pairs conspicuously natatory, having fifth and sixth joints 

 flattened and somewhat or feebly expanded, with a moderate or low number of natatory sette, and 

 seventh joint well developed. — Abdomen at most with a rudimentary basal segment; uropods ventral, 

 the endopod unjointed, frequently moderately long, the exopod short or wanting. 



Remarks. This group comprises three genera hitherto established, viz. Drsmosoma G. O. Sars, 

 Eugerda Meinert and Echinopleura G O. Sars, but for reasons given later on I cancel Eugerda and 

 refer its species to the large genus Desmosoma. The group occupies in certain features a position 

 between the Nannoniscini and the Ilyrachniui, but differs materially from both in several characters, 

 especially in the legs. The head has a more or less developed "front area" as described in the 

 Nannoniscini. 



Desmosoma g. o. Sars. 



This genus has, on the whole, been well characterized by Sars, but I must cancel the genus 

 Eugerda Meinert adopted by Sars. On Desmosoma, as limited in the present paper, some points may 

 be mentioned. 



The anteunuke have in the flagellum 2 joints, in the male of a single species 3 joints, when 

 the peduncle is considered as 3-jointed. At the lateral margins of the four anterior thoracic segments 

 epimera are always visible, and at least on second to fourth segment always marked off by a suture, 

 while such a suture is sometimes distinct, sometimes not discernible, between first segment and the 

 epimera; the shape of the epimera, especially of first and second pairs, affords excellent characters, but 

 it must be added, that in some species (f. inst. I), longispinum: PI. X, figs. 6 a and 6 e) the epimera 

 are somewhat or considerably more produced in the male than in the female. At the margins of the 

 three posterior segments no epimera are found; these segments are frequently proportionately broader 

 or sometimes narrower in the male than in the female; besides, the shape of fourth segment may 

 differ according to sex (PI. XI, figs. 5 b and 5 c). In D. laterale G. O. S. the four anterior segments 

 have on the ventral surface a long, spiniform process in the median line; in D. longispinum a small 

 process protrudes obliquely forwards on first segment, and in some forms no ventral armature is found, 

 but the feature has not been examined in several species. 



First and second pairs of thoracic legs differ so much in shape and adornment with setae or 

 spines from species to species, that they afford some of the best characters, and must always be care- 

 fully studied. First pair are in some species considerably or extremely slender, and their use seems 

 to be somewhat uncertain, while in other forms they are thick and, sometimes, even very strong pre- 

 hensile organs. Second to fourth pairs are to some degree similar in structure, but second pair are 

 stronger and more peculiar than the third, and especially than the fourth pair. To the brief descrip- 

 tion above of the three posterior pairs of legs may be added that in the male of D. uatator (PI. XI, 

 fig. 2 d) these legs are on the whole rather similar to the same legs in males of some species of Nan- 



