THE DIASTYLID® oll 
1780, it possesses the earliest in date of the Cumacean 
species, unless the doubtful Gammuarus esca, Fabricius, 
1779, be allowed precedence. The name is evidently 
based on a Greek word meaning ‘ with an interval between 
the columns,’ and in this Greek word the penultimate 
syllable is long, but the interval referred to is not really 
between columns, as implied by the Greek styli, but 
between the stilets or slender-branched uropods, to which 
the Latin word stili is appropriate. But to pronounce the 
name as Diasti#lis in accordance with this correction would 
make a hybrid of it, and it cannot therefore be recommended. 
This genus has the second antenne in the male very fully 
developed, attaining the length of the body. The third 
and fourth perzeopods in the female have no rudimentary 
exopods. The genus is widely distributed, and includes 
thirty species or more. Several of these are recorded by 
Norman, Robertson, and others, from British waters, as : 
Diastylis Rathkit (sroyer), Diastylis cornuta, Boeck, Dia- 
stylis insignis, Sars, Diastylis echinatus, Spence Bate, Dia- 
stylis biplicata, Sars, Diastylis spinosa, Norman, Diastylis 
levis, Norman, Diastylis rugosa, Sars, Diastylis tumidu 
(Lilljeborg), Diastylis lamellata, Norman. 
Leptostylis, Sars, 1869, has the second antennz of the 
male less fully developed than in the preceding genus, 
and has rudimentary exopods on the third and fourth 
pereeopods in the female. ‘The genus includes six species, 
of which Leptostylis producta, Norman, is British. 
Diastylopsis, S. I. Smith, 1880, like Diastylis, has no 
rudimentary exopods on the third and fourth perzeopods of 
the female, but it is distinguished by the unique character 
of having the third and fourth free segments of the perzeon 
consolidated. To the American species, Diastylopsis Daw- 
soni, Smith, must be added Diastylopsis resima (Kroyer), 
which is well marked by the upturned nose or pseudo- 
rostrum, to which the specific name refers. 
By aid of the accompanying table the student will be 
able to assign his specimens to their proper families, which 
will be found a very useful preliminary to the more difli- 
cult task of discovering the genus and the species :— 
