THE DIASTYLIDiE 311 



1780, it possesses the earliest ia date of the Cnmacean 

 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 Biastylis 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 perseopods 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 : 

 Diastijlis Rathkii (Kroyer), Diastylis cornuta, Boeck, Bia- 

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

 stylis hipUcata, Sars, Biastylis spinosa, Norman, Biastijlis 

 Iceuis, Norman, Biastylis rugosa, Sars, Biastylis tumiJn, 

 (Lilljeborg), Biastylis l-amellata, Norman. 



Leptostylis, Sars, 1869, has the second antenna) of the 

 male less fully developed than in the preceding genus, 

 and has rudimentary exopods on the third and fourth 

 perseopods in the female. The genus includes six species, 

 of which Leptostylis proJuda, Norman, is British. 



Biastijlopsis, S. I. Smith, 1880, like Biastylis, has no 

 rudimentary exopods on the third and fourth peraeopods of 

 the female, but it is distinguished by the unique character 

 of having the third and fourth free segments of the perason 

 consolidated. To the American species, Biastylopsis Baw- 

 snni, Smith, must be added Biastylopsis 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 difS- 

 cult task of discovering the genus and the species : — 



