MYSIDEA. 659 



Plate 44, fig. 1 a, male, enlarged ; b, posterior part of thorax of 

 female, more enlarged ; c, extremity of abdomen ; d, first maxilla ; e, 

 maxilliped ; /, first pair of legs ; /', fouette, attached at base ; g, one 

 of posterior legs. 



Pacific, near St. Augustine's Island ; also, near Pitt's Island, Kings- 

 mills Group. Collected, March 25, 1841, and April 30, 1841 ; also, 

 latitude 15 north, longitude 180 west, December 9, 1841. 



Length, two and a half lines. Colourless. The last abdominal 

 segment is but little shorter than caudal lamella adjoining, and the 

 eyes are much smaller than in the vitrea. The outer caudal lamella 

 is hardly shorter than the inner. The hairs extend back some dis- 

 tance on outer side, and rapidly diminish in length, the last being the 

 shortest and quite minute ; hairs at extremity are nearly half the 

 length of the lamella. The inner lamella has a stout, longish spine at 

 apex, besides hairs on the margins. Diameter of eyes scarcely more 

 than half the breadth of the abdomen at its base. Basal scale of 

 outer antennae reaches a little beyond apex of base, and the base ex- 

 tends half its length beyond the eyes. Hairs on under side of flagel- 

 lum few and not longer than diameter of joints. Shorter flagellum of 

 first antennas have on basal half two distant minute spines. 



An ensiform lamella (fouette, fig. /) attached to base of first pair of 

 legs and kept in constant vibration under the carapax. Reniforrn 

 gland in thorax small in male (see figure), but very large oblong in 

 female ; it was nearly as long as thorax and two-thirds as broad. 



A specimen of Siriella collected in the Sooloo Sea (Plate 42, fig. 2 a, 

 b, c), has the general characters of the gracilis, the eyes (fig. a) a little 

 larger, the caudal lamellas (fig. V) equal, and the caudal segment as in 

 the gracilis, the hairs of the lamellae quite long, and extending up on 

 outer side of outer lamella some distance from extremity, with the 

 last of the hairs short like spinules, and the very last one the shortest 

 of all; the front prominent triangular; the basal scale of outer an- 

 tennas extending as far forward as the base of inner antennas. The 

 specimen is a male, and has a prominent tooth or spine on the lower 

 side of the sixth abdominal segment (fig. c), a character not observed 

 by us in the male of the gracilis. 



