I I 



the last-named feature is also seen in the Petalophthalmicke and in some of the Lophogastrida. 

 In the Boreomysinae the major distal part of the outer margin of the exopod is furnished with 

 seta? as on the distal joint of the Siriellinae and the Petalophthalmidee, while the proximal part 

 is naked with a couple of spines at its distal end, and at these spines a feeble vestige of the 

 transverse articulation is observed; in Boreomysis inerinis n. sp. the naked part is extremely 

 short and the spines seem to be wanting (PI. II, fig. ^ó). In the Gastrosaccinae the exopod 

 has no vestige of an articulation but its outer margin is furnished either with a number of 

 spines {Anchialina, Gastrosacctts) or with a couple of spines beyond the middle (Paranchialina) 

 or with a single spine near its end (Pseuda?ichialma), and setee between the spine or spines 

 and its base are always wanting. In the Mysinae and the Mysidellime the exopod has no vestige 

 of an articulation and no spines but common setae along its outer margin. 



An otocyst is always wanting in the endopod of the uropods in the Lophogastridae and 

 Petalophthalmida-, but probably always present, though sometimes rudimentary, in the Mysidae. 



T e 1 s o n. — It presents infinite variation as to shape and armature and is consequently 

 of high value for separation of genera and species, but shows scarcely any feature of higher 

 systematic importance, though its shape can be used in the description of the small subfamilies. 



It may be seen from this detailed account that among the structural differences mentioned 

 some of those derived from the number of the marsupial plates, the exopod of the uropods, 

 the pleopods in the male, the thoracic legs and the labrum are of higher value for dividing the 

 family into natural subfamilies and tribes, while the differences found in scutum, eyes, antennulae, 

 antenna?, mouth-appendages and telson as a rule cannot be used for finding out relationship or 

 defining such groups of higher order. It is attempted here to give a synopsis of the subfamilies 

 and tribes. 



A. Seven pairs of marsupial plates in the female. 



Labrum broader than long, without front process. Thoracic legs with 

 sixth joint divided by one or two vertical articulations. Pleopods well 

 developed; exopod of second and third pairs elongated. Exopod of uropods 

 with the proximal part of the outer margin naked and generally with a 

 couple of spines and a transverse rudimentary articulation at the end of 

 the naked part. (Telson distally cleft) Subfamily I. Boreomysina-. 



B. Three or two pairs of marsupial plates in the female. 



a. Exopod of uropods with a feeble or sharp articulation beyond the middle. 

 2. Labrum much longer than broad, with a very long front process. 

 Thoracic legs with sixth joint undivided or, generally, divided by 

 a single articulation and terminating in a brush of stiff, peculiarly 

 serrated setae surrounding the "claw" as usually consisting of seventh 

 joint and the real claw and very strong (except in first pair of Hemi- 

 siriella). Pleopods well developed, with biramous pseudobranchiae 

 and their rami sausage-shaped ; the four posterior pairs either similar 

 or the endopod or both rami of fourth pair or the endopods of 



