34 



The species of Acetes live near the coasts, sometimes in the estuary of large rivers or 

 even in such rivers, generally in tropical and subtropical seas or countries, but yet going so 

 far northwards as to Korea. The different species are similar in general aspect and therefore a 

 careful investigation is necessary; probably there exist still a good number of undiscovered 

 forms, and the geographical distribution of each species seems to be somewhat or much restricted. 

 Judging from my material numerous specimens can frequently be taken in the same haul. 



I. Species from Asia. 



In all species from the seas south and east of Asia known to me the rostral crest has 

 two denticles behind the acute tip. In the female the antennal squama reaches to, or distinctly 

 beyond, the middle of third joint, but is far from reaching the end; in this sex the coxae of 

 third pair of legs have always a somewhat large, protruding tooth on the distal inner angle, 

 while the inner margin of the coxae is concave, and the proximal inner corner is produced into 

 a flat, rounded protuberance. 



It is easy to give a key to the males, but as to the females it is preferred' to make it 

 somewhat imperfect, because one of the best specific characters is the shape and structure of 

 the genital area, which is next to impossible to deal with in a key. 



Key to the Males. 



A. Antennular peduncles with the third joint not much longer than in the 

 female, only about half as long again as the inner margin of second joint, 

 and shorter than the lower flagellum. The antennal squama reaches 

 rather considerably beyond the end of second antennular joint. (Petasma 

 has a well developed pars astringens with marginal coupling hooks). 



a. Coxae of third lees with a triangailar tooth on the distal inner 

 angle. In the petasma the capitulum is scarcely one-third as long 



again as processus ventralis A. vulgaris n. sp. 



b. Coxae of third legs without any tooth on the distal inner angle. 

 In the petasma the capitulum is elongated, about twice as long 



as processus ventralis Acetes sp. 



B. Antennular peduncles with the third joint very much longer than in 

 the females, between twice and three times as long as the inner margin 

 of second joint and at least almost twice as long as the lower flagellum. 

 The antennal squama reaches scarcely or slightly beyond the end of 

 second antennular joint. 



a. Trochanter of third pair of legs without any tooth on the inner 

 margin near its end. 



a. Ciliated part of the outer margin of the exopod of the 

 uropods conspicuously shorter than the glabrous part. 



