THE DIASTYLID/E 311 



1780, it possesses the earliest in date of the Cumacean 

 species, unless the doubtful Gammarus escdj 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 st5di, 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 antennse in the male very fully 

 developed, attaining the length of the body. The third 

 and fourth pergeopods 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 w^aters, as : 

 Biasti/Us RathJdi (Kroyer), Diastylis cornuta, Boeck, Dio,- 

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

 stylis biplicaia, Sars, Diastylis spinosa, Norman, Diastylis 

 Icecis, Norman, Diastylis rugosa., Sars, Diastylis tumida 

 (Lilljeborg), Diastylis lamellaia, Norman. 



Lejytostylis, Sars, 1869, has the second antennas of the 

 male less fully developed than in the preceding genus, 

 and has rudimentary exopocls on the third and fourth 

 per^opods 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 pera^opods of 

 the female, but it is distinguished by the unique character 

 of having the third and fourth free segments of the per^eon 

 consolidated. To the American species, Diastylopsis Daw- 

 soni, Smith, must be added Diastylopsis reslma (Kroyer), 

 w^hich 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 : — 



