6 



yet in Mysis (Neomysis) vidgaris Thomps. its very convex front margin has a moderately short, 

 conical process, thus being to some extent an exception from that in the other Mysinse. 



Mandibles. - In the Mysidellinse these appendages are quite anomalous (comp. G. 

 O. Sars, Norges Mysider). In several genera the cutting edge, the movable lacinia, the setse 

 and the molar process are well developed, but frequently one or two of these elements are 

 less or more reduced or sometimes quite lost; the characters shown by the numerous differences 

 in these parts seem, however, as a rule to be only of generic value. The joints of the palps 

 present minor differences of generic value; in a single genus, Lycomysis n. gen., the inner part 

 of the second joint is expanded, firmly chitinised, with a row of sharp saw-teeth, certainly 

 constituting an auxiliary instrument for dealing with the food. 



Maxillulse. — In the Mysidellinae (the genus Mysidella G. O. S.) they are aberrant 

 (comp. G. O. Sars), otherwise they are somewhat uniform, presenting sometimes smaller differences 

 of eenene value. 



Maxillee. — They are somewhat uniform in the vvhole family, the lobe from second 

 joint, the size of the exopod, the size and shape of the last joint of the palp show characters 

 of generic, but not of higher, value. 



Maxillipeds. — In Arachnomysis Chun these appendages have no epipod, in Arach- 

 nomysis Chun and in Ccrsaromysis Ortm. the exopod is wanting; in all other genera both the 

 epipod and the exopod are well developed. The endopod (the two proximal joints included) shows 

 numerous differences in the size and direction of the second joint, in breadth and furniture with 

 setse or spines of the following joints, in the number of lobes and in the development or 

 existence of the claw. In some genera the second joint has no lobe; in the majority this joint 

 has a free lobe varying much in size; in some genera the third joint is also provided with a 

 lobe, and in some forms (f. inst. in Mysis oculata O. Fabr.) the second joint has a large lobe, 

 third and fourth joints each a lobe of considerable size. In Mysidopsis G. O. S. second and 

 third joints are coalesced (according to G. O. Sars), and in Mysidella G. O. S. the distal joints, 

 especially sixth joint, are aberrant (see below). The characters derived from the more essential 

 differences are always of generic and sometimes of somewhat higher value ; thus it may be 

 pointed out that a lobe from the third joint is wanting or small, a lobe on fourth joint always 

 wanting in the genera which in more important characters are related to the lower families 

 of the order. 



Gnathopods. — For practical reasons I apply this name, because these appendages, 

 in reality the first pair of thoracic legs, being as a rule intermediate in structure between the 

 maxillipeds and the following legs, are to be mentioned separately many times in the following 

 descriptions. The gnathopods show differences essentially of the same nature as those found in 

 the maxillipeds, with the exception that lobes are never so highly developed as on the latter 

 appendages in many forms: the lobe from second joint, if present, is generally broad and 

 somewhat short, a lobe from third joint is never found, and only in Mysidcis G. O. S. a kind of 

 short lobe is developed on fourth joint. In Arachnomysis Chun the gnathopods are elongated, 

 exceedingly strong, and seventh joint with the claw can be bent against the terminal part of 

 the sixth joint; in Eucha-iomcra G. O. S. the last-named peculiarity begins to develop ; in 



