364 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxm. 



g. Third dorsal plates covering less than half the genital segment, their margins 

 smooth; fifth legs invisible; abdomen partly visible. 



perspicax Olsson, 1869, p. 364. 

 h. Third dorsal plates covering nearly the whole genital segment; no spines at 

 their anterior corners; posterior lobes of the genital segment turned 

 strongly inward and almost touching each other; fifth legs invisible. 



torpedinis, new species, p. 371. 



h. Third dorsal plates covering about two-thirds of the genital segment, spines 



at their anterior corners; posterior lobes of tlie genital segment parallel and 



separated by a wide sinus; fifth legs visible beyond the tips of the lobe. 



neozcalanicus Thomson, 1889, p. 365. 

 i. Carapace three times the width of the genital segment; frontal plates broad and 

 prominent; third thorax segment as wide as the fourth. 



perspicax Olsson, 1869, p. 364. 



i. Carapace two and a half times the width of the genital segment; frontal plates 



very small and narrow; fourth thorax segment short, wider than the genital 



segment and semilunar neozcalnnicus Thomson, 1889, p. 365. 



i. Carapace twice the width of the genital segment; frontal plates wide and promi- 

 nent; fourth thorax segment long and narrower than the genital segment. 



braccatus Dana, 1852, p. 366. 



This genus was established by Steenstrup and Llitken in 1861 

 to inchide, as they said, four species which had up to that time 

 been classed with the genus Dinematura, namely D. alata Milne 

 Edwards, D. affinis Milne Edwards, D. coleoptrata Guerin, and 

 D. hraccata Dana. These agree with each other and differ from 

 the true Dinematura species in the following: (1) The first two free 

 thorax segments are fused together; (2) the genital segment is 

 broad and flat, not long and narrow; (3) the dorsal plates are larger 

 and cover half the genital segment or more; (4) the abdomen is not 

 jointed, it carries only a single dorsal plate, and it is often con- 

 cealed beneath the genital segment; (5) the fourth swimming legs 

 are small and their basal joints are not wing-like when developed; 

 (6) the first three pairs of legs do not deserve the name of swimming 

 legs, and their plumose setse are poorly developed. 



The authors might have added a seventh difference which would 

 have been at least as valuable as any of the others. In Dinematura 

 the sixth thoracic segment is well separated from the genital seg- 

 ment, and it bears a pair of dorsal plates and also a rudimentary 

 pair of swimming legs. In EcJithrogaleus , on the other hand, this 

 sixth segment is reduced to a mere lobe attached to the base of the 

 posterior sinus of the genital segment, and there is not even a trace 

 of any dorsal plates or swimming legs. To this genus EcJithrogaleus 

 belong also the following five species, which have appeared since 1861 : 



^^ Dinematura^ ^ indistincta, described by Kroyer in 1863 (p. 183), 

 but of which no figures have ever been published; rightly referred 

 to the present genus by Bassett-Smith in 1899. 



Echthrogaleus perspicax, described by Olsson in 1869; includes 

 both sexes and is well illustrated. 



