M Y S I D E A. 055 



maturity, from the undeveloped egg, to the young with jointed mem- 

 bers. The different states observed are represented in figures g to m. 

 On the llth of December, these young were found abundantly, and 

 nearly all the specimens obtained were females. On the 24th of the 

 same month, no gravid females could be found, and at the same loca- 

 lity not more than six adults out of a hundred specimens. They were 

 in general about half grown, being one-tenth of an inch long, instead 

 of one- third, the usual adult size, and none had ovarian pouches. In 

 adult males, the scales of the ovarian pouch are replaced by very 

 short organs situated nearly between the bases of the preceding pairs. 

 Abdominal appendages of first three segments, short, and close ap- 

 pressed to the venter ; of fourth segment, long and slender, consisting 

 of a two-jointed basal portion, with which is articulated a slender ex- 

 tremity, having two small joints towards its extremity and termina- 

 ting in two unequal setae. This organ reaches back a little beyond the 

 extremity of the body. 



GENUS SIRIELLA, Dana. 



Carapax mx rostratus. Rdes thoracici numero sexdecim, toti biramei ; 

 palpo elongate basi valde lato flagelloque, multiarticulato ; ramo pedi- 

 formi unguiculato, b-articulato (unyue iticluso). Oculi fere orbiculati. 

 Antennas internee biramece, external flagello cwifectce lamindque oblongd 

 basali. Appendices abdominales rudimentarii. Segmentum abdo- 

 minis postremum apice rotundatum et spinulis ciliatum. 



Carapax hardly rostrate. Thoracic feet eight pairs, all two-branched, 

 the palpus elongate, and consisting of a very broad basal joint and 

 a multiarticulate extremity, the main branch unguiculate, five- 

 jointed (claw included). Eyes nearly orbicular. Inner antennae 

 two-branched ; outer ending in a flagellum and having an oblong 

 scale at base. Abdominal appendages all rudimentary. Posterior 

 segment of abdomen rounded at apex, and ciliate with minute 

 spinules. 



These species have a pouch for the young, under the posterior part 

 of the thorax, like those of Mysis. Yet they differ, in having eight 

 pairs of feet, and all unguiculate. The last abdominal segment is 



