270 A HISTORY OF RECENT CRUSTACEA 
generally unlike those in the other sex, but the three re- 
maining pairs usually simple and rudimentary like the 
pleopods of the female. The telson is either incised or whole 
at the apex. The very numerous species may be distin- 
guished by the general shape, by the structure of the scale 
of the second antenne and its size in relation to the 
peduncle of the first antennze, by the number of articulations 
in the subdivided joint of the trunk-legs, by the shape of 
the telson and its length in relation to the uropods, and by 
the structure of the fourth pleopods in the male. 
Several of the species occur in British waters, but only 
two of them are definitely described in Bell’s ‘ History of 
the British Stalk-eyed Crustacea,’ namely Mysis jlexuosus 
(Miiller), under the name of Mysis chameleon, J. Vaughan 
Thompson, which has the telson incised, and Mysis vulgaris, 
Vaughan Thompson, which has the apex of the telson un- 
divided, and which may be the same as the Prawnus i- 
teger of Leach, from Loch Ranza. Mysis neglecta, Sars, 
has been taken by Norman at the Channel Islands, and is 
reported by Dr. Henderson from the Clyde. Meinert 
does not feel sure that it is distinct from Mysis flexcuosus, 
he having often met with individuals which seemed to 
be links between the two. Norman groups them both 
with Mysis inermis, Rathke, a species found in Shetland, 
observing that all three are distinguished by an antennal 
scale which is long, lanceolate, subparallel-sided, and having 
the apex scarcely produced beyond the unciliated external 
margin, but that in flecuosus the scale is seven or eight 
times as long as broad, in neglecta about five times, in 
imermis about four times. Mysis spiritus, Norman, has 
the eyes on long stalks, the spines on the inner branch 
of the uropods closely crowded, the fourth pleopods in the 
male ‘ with the first three joints subequal in length, and 
the last joint subequal to the fourth.’ On the other 
hand, Mysis ornata, Sars, has the eyes short, the spines on 
the inner branch of the uropods not crowded, the fourth 
pleopods in the male, with ‘the outer branch very like 
that of M. spiritus, but the third joint is much longer than 
either of the two first, which are subequal ; fifth joint not 
. a 
