Anchialina Norm. some of the distal joints are peculiarly developed in the male, normal in 

 the female. 



Six Pairs ofthoracic Legs. — In the suborder Lophogastrida and in the family 

 Petalophthalmidae the sixth joint is always undivided; in the Mysidae it is generally divided 

 into subjoints, but their number is very different. In the Siriellinoe this joint has only a single 

 articulation, which is transverse or oblique, at most allowing a slight lateral flexion ; in some 

 few species I have been unable to find this articulation which seems to have disappeared. In 

 all other Mysidae the sixth joint of the thoracic legs has at least a transverse more movable 

 articulation beyond the middle (the very thick first pair in Heteromysis Smith has the joint 

 undivided); in a good number of genera (f. inst. Erythrops G. O. S., Parcrythrops G. O. S., 

 Pseudomma G. O. S., Amblyops G. O. S., Holmesiella Ortm., that is to say in the genera 

 constituting the rich tribe Erythropini mihi) it has one distal vertical and generally a somewhat 

 more proximal oblique articulation; in Boreomysis G. O. S. it has at least one, generally two 

 vertical articulations, in Mysidella G. O. S. it has — according to Sars — one vertical articulation 

 on the first pair and two on the following pairs, in Mysidopsis G. O. S., Mysideis G. O. S., 

 Mysideies Holt. & Tatt. and Lcptomysis it has two vertical articulations, in Hcmimysis abyssicola 

 G. O. S. it has — according to Saks — three articulations on the five anterior pairs and four 

 on the last pair; in some species of the sübfamily Gastrosaccinae and of the genus Mysis sens. 

 Sars 1879 the number of articulations is still higher. In genera consisting of very small species 

 of the Gastrosaccinse and the tribe Mysini the number of these secondary articulations is lower 

 than in genera consisting of larger or large species. But on the whole the number and direction 

 of these articulations is of interest, because they are to be considered as secondary divisions 

 of a joint undivided in the lower families of the order. 



In the sübfamily Siriellinae the seventh joint and the claw are very strong except on 

 first pair in Hemisiriella n. gen., in many other genera the same elements are less strong but 

 yet well developed, while in some genera [Rhopalophthalmus Illig, Anchialina Norm.) both 

 are either rudimentary or even impossible to point out. In the Siriellinae the end of sixth joint 

 is furnished with a brush of strong setse serrated in a most peculiar way (to be described in 

 the definition of the sübfamily); in Hemisiriella n. gen. the first pair of legs are extremely 

 elongated in both sexes; in Heteromysis Smith the legs of first pair are strong, prehensile 

 organs; in the male of some species of Anchialina Norm. the first pair are distally developed 

 in an aberrant way showing characters of specific value. 



Marsupium. — In the Lophogastrida and Petalophthalmidae it consists of seven pairs 

 of lamellae. Among the Mysidae this number has been preserved in Boreomysis G. O. S., which 

 also in a few other features shows kinship to the lower Mysidacea. In all other Mysidae only 

 three or two pairs (? one pair) of marsupial plates are found. 



Abdominal Segment s. — In nearly all — perhaps in all — Gastrosaccinae the first 

 segment has a pair of lateral lamellae, sometimes quite small {Anchialina typica Kr.), in other 

 forms (Gastrosaccus Norm.) very large, as a kind of partial covering or support of the marpusium. 

 There is no tracé of these lamellae in any other sübfamily. 



Pleopods. — A. Female. In the Lophogastrida all pleopods are well developed, 



