222 



as a rule, very small and sometimes greatly reduced in number. In the male, 

 the more or less complete fusion of the 1st segment of mesosome with the ce- 

 phalon is a very pronounced character, and moreover the larva in the last (Cryptonis- 

 cian) stage exhibits several well-marked peculiarities first pointed out by Dr. 

 Hansen. All the hitherto known forms are found parasitic on Schizopoda belong- 

 ing partly to the family Euphausiidce, partly to that of the Mysidce. We know 

 at present of only 4 genera belonging to this family, 3 of which will be treated 

 of below. 



Gen 1. DajUS. Kr0yer, 1842. 



Syn. : Leptophryxus, Buchliolz. 



Generic Characters. — Body of adult female very tumid, slightly curved 

 ventrally, with the lateral parts greatly expanded and more or less projecting in 

 front beyond the cephalon, middle part of dorsal face sub-depressed and distinctly 

 segmented. Metasome abruptly contracted and divided into 6 segments, the last 

 carrying 2 small juxtaposed lamella?, the uropoda. Oral area comparatively 

 broad, semicircular. Antennae distinct, and of normal structure. Maxillipeds 

 extended anteriorly, as in the Bopyrida?. Sternal plate of moderate size, trigonal 

 in form. Incubatory plates present in the normal number (5 pairs), last >air 

 much the largest. Legs short and thick, exactly alike. First pair of pleopoda 

 forming 2 rather large lamella? occurring immediately behind the last pair of in- 

 cubatory plates; the succeeding pairs rudimentary. — Adult male with the meta- 

 some undivided. Parasitic on species of the genera Mysis (sens, strict.) and 

 Cynthilia (Siriella), being attached to the ventral face of the last segment of 

 mesosome, between the incubatory lamellae of the host. , 



Remarks. — This genus was established in the year 1842 by Kroyer, to 

 include a peculiar parasite found by him on a species of Mysis. The genus 

 Leiitoiihryxus of Buchholz is unquestionably identical with Kroyer's genus, and 

 was founded upon the very same species. We know as yet of only 2 species be- 

 longing to this genus. One of these will be described below, the other having 

 been briefly recorded from the Challenger Expedition by the present author, 

 under the name of Dajus siriellce. A 3rd species, it is true, has been estab- 



