270 A HISTOKY OF EECENT CEUSTACEA 



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 apes. The very numerous species may be distin- 

 guished by the general shape, by the structure of the scale 

 of the second antenna and its size in relation to the 

 peduncle of the first antennae, 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 flexuosm 

 (Miiller), under the name of Mysis chamceleon, 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 Praunus in- 

 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 flexuosus, 

 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 flexuosus the scale is seven or eight 

 times as long as broad, in neglecta about five times, in 

 inermis about four times. Mi/sis 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 



