THE DIASTYLID^ 311 



1780, it possesses the earliest in date of the Cumacean 

 species, unless the doubtful Gammarus 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 Diastylis in accordance with this correction would 

 make a hybrid of it, and it cannot therefore be recommended. 

 This genus has the second antennae in the male very fully 

 developed, attaining the length of the body. The third 

 and fourth perasopods 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 Ratlikii (Kroyer), Diastylis cornuta, Boeck, Dia- 

 stylis insignis, Sars, Diastylis echinatus, Spence Bate, Dia- 

 stylis biplicata, Sars, Diastylis spinosa, Norman, Diastylis 

 Icevis, Norman, Diastylis rugosa, Sars, Diastylis tumida 

 (Lilljeborg), Diastylis lamellata, Norman. 



Leptostylis, Sars, 1869, has the second antennse of the 

 male less fully developed than in the preceding genus, 

 and has rudimentary exopods on the third and fourth 

 perasopods 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 perseopods of 

 the female, but it is distinguished by the unique character 

 of having the third and fourth free segments of the pereeon 

 consolidated. To the American species, Diastylopsis Daw- 

 soni, Smith, must be added Diastylopsis reslma (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 diffi- 

 cult task of discovering the genus and the species : 



