268 REPoRT—1868. ~~ 
second, third, fifth, or seventh) with smaller spines, the rounded entire 
apex terminating in four spines, the outer pair much longer than the 
middle pair; on examining the telson from below, it is seen to form, 
for about half its length, an open tube, the opening consisting of a 
central slit, the margins of which are edged with small spines. Interior 
lamellz swollen at the base for the reception of the acoustic organ, but 
afterwards very narrow, slightly longer than telson. Outer lamelle 
remarkably long and very narrow, fully half as long again as inner 
pair; both margins of both pairs fringed throughout with long plumose 
sete ; inner margin of inner lamellz also closely beset with spines, 
which are of unequal size. 
In the male, the superior antenne have the last joint of the pedun- 
cle furnished with the usual lobe and dense tuft of hair. All the pleo- 
pods have a stout, large basal joint, which gives support to two branches, 
the inner of which in the last four pair is multiarticulate and setose, 
and gives off, close to the base, a small lateral lobe terminating in short- 
sete, but in the first pair the inner branch is rudimentary. The outer 
branch in the first three and the last pair is also multiarticulate and 
setose, but in the fourth pair is a more complicated organ, and consists 
of six joints at the base, all furnished on each side with a long plumose 
seta, and two branches of equal length, one slender, one-jointed, of 
equal thickness throughout, ciliate, the other having a much stouter 
basal joint and two multiarticulate ciliated filaments. 
A single male in 40-50 fathoms, 5-7 miles off Balta, in 1857 ; and 
both sexes previously sent to me by Mr. Edward from Banff. 
The descriptions of Mysis gracilis and M. linguura, G. O. Sars, come 
very near to the female of this species, but the present is at once dis- 
tinguished by haying the antennal scale two- and not three-jointed. 
Genus Gasrrosaccus, Norman. 
A genus of Mysidea. Female: marsupial pouch attached to last segment of 
pereion and first of pleon. First pleopod composed of a much elongated basal 
joint, and two short one-jointed branches; second to fifth pairs consisting 
of a single joint. Male having all the pleopods consisting of a basal joint, 
and two branches differently developed on the different segments, and the 
third pleopod the greatly developed sexual organ. 
Gastrosaccus sanctus (Van Ben.)=Mysis sancta, Van Beneden, Recherch. sur 
la Faune Litt. de Belgique, Crustacés (1861), p. 17, pl. vii. figs, 1-4 
(the male), = Mysis spinifera, Goes, Crust. Decap. Podophth. marina 
Suecie (1863), p. 14 (the female),= Gastrosaccus sanctus, Norman, Rep. 
Brit. Assoc. 1867 (1868), p. 438. 
Female.—Sides of carapace extending much beyond the dorsal portion, 
which has its margin elegantly scalloped; fifth segment of pleon pro- 
ducing backwards on the back into a well-developed spine. Rostrum 
slightly produced, rounded at the extremity. Eyes cylindrical, on short 
peduncles. Superior antenne with greatly developed peduncles; first 
joint as long as two following, cylindrical, smooth; second joint half 
length of last, with three large spines in a longitudinal row on the 
outer margin ; filaments long and slender, the outer with its first joint 
long (equal about eleven of inner), and furnished on its inner face with 
a cutaceous process, apically setose, which reminds us of the lobe of the 
males of Mysis. Inferior antenne having peduncle reaching the last 
joint of peduncle of superior antenne ; scale short, subequal in length 
