Mysidacea, Tanaidacea and Isopoda. 
411 
nine specimens up to 10 mm. A note on the label reads "Water fresh permanently, 
but affected strongly by tide. Very muddy. Bottom firm sandy mud" and a further 
label says that this species was " only caught at or near the bottom." 
It is with' some doubt that I refer these specimens to Neomysis nigra, Nak. 
Though the specimens measure up to 10 mm. in length, the males are still immature, 
to judge by the condition of the fourth pair of pleopods. Nakazawa's .specimens, 
though measuring only 7-8 mm, were, from his description, fully mature. But 
otherwise I have failed to find an)^ noteworthy point of difference and I tentatively 
refer them to this species until more material is available. 
I may perhaps be allowed to supplement Nakazawa's description in a few 
particulars. 
The segments of the pleon diminish successively in size from the first to the 
fifth, and the sixth segment is one and a half times as long as the fifth. 
The telson (PI. XV, fig. 6) is slightly longer than the last segment of the pleon. 
It is one and a half times as long as broad at its base. The apex is truncate, one 
quarter as broad as the base of the telson, and bears two pairs of spines, an inner 
shorter pair and an outer longer pair, which are about as long as the apex of the 
telson is wide. The lateral margins bear 18-19 spines extending the whole way 
down their length. 
The inner uropod is about one and a half times and the outer uropod nearly 
twice as long as the telson. 
I have given a figure of the telson and the eye of one of my specimens for com- 
parison with the same parts of N . awatschensis, Brandt, a very closely allied species, 
also occurring in this collection. The two .species differ in the following points : — 
(1) In A^. nigra the ro.strum is broadly triangular with a pointed apex. In 
N. awatschensis the rostrum is a broadly rounded plate. 
(2) N . nigra appears to have a broader and stouter e5^e than in N. awatschensis. 
In A' . nigra the eye is slightly less than one and a half times as long as 
broad, with the peduncle half as wide as the eye is long and the pigment 
occur>ying the distal half of the eye (PI. XV, fig. 5). In N . awatscJiensis, 
^ the eye is rather more than one and a half times as long as broad, the 
peduncle only | as wide as the e5'^e is long and the pigment occupying less 
than half of the eye, (PI. XV, fig. 2). 
( ',) In the form of the fourth pleopod of the male. 
In my most mature male, the fourth pleopod does not extend the whole 
length of the last segment of the pleon and has the first joint of the outer 
branch only one and a half times as long as the second, while the terminal 
setae are only two-thirds the length of the last joint. 
Nakazawa says that the outer branch of the fourth pleopod of the male 
reaches to the middle of the telson, that its proximal joint is four times 
as long as the distal and that the terminal filaments are longer than the 
distal joint. 
