in a few genera only the distal articulation preserved. Four 

 posterior pairs of male pleopods well developed ; exopod of 

 fourth pair rarely and at most slightly elongated, endopod 

 of the same pair sometimes elongated, and in several genera 

 one of these rami with peculiar sets. Antennal squama nearly 

 always with a pronounced external tooth, and even if this is 

 wanting at most the distal half of the outer margin adorned 

 with some few setee ; in a few genera the squama is styliform 



or wantino- Tribe i. Erylhropini'^). 



§§. -Si.xth joint of thoracic legs with two, rarely three, vertical 

 articulations and no oblique articulation. Four posterior pairs 

 of male pleopods either rudimentary [JMysidetes Holt & Tatt.) 

 or, generally, well developed; exopod of fourth pair either 

 elongated or terminating in a thick spine while the endopod 

 is always normal. Antennal squama lanceolate, frequently much 

 produced, with the outer margin setiferous to its base. Tribe 2. Leptomysini. 

 §§§. Sixth joint of thoracic legs without any oblique articulation, 

 generally with two or three or more vertical articulations. At 

 least second male pleopods rudimentary and the exopod of 

 fourth pair always very elongated. Antennal squama extremely 



varying Tribe 3. Mysini. 



§§§§. First pair of thoracic legs strongly thickened, with the sixth joint 



undivided, very thick, spiniferous ; sixth joint of the following 



pairs with several vertical articulations. All pleopods in the 



male rudimentary. Antennal squama oblong-oval. Tribe 4. Heteroniysini. 



If. Labrum posteriorly produced into a large plate divided by a 



deep incision into two lobes unequal in size. Mandibles with the 



cutting lobe very expanded and its edge straight, without teeth; 



maxillulse with the lacinise bent strongly inwards; maxillipeds 



with their sixth joint expanded and possessing a free distal margin 



with some spines. (Sixth joint of first pair of thoracic legs with 



one, of the following pairs with two vertical articulations. Male 



pleopods rudimentary) Subfamily VI. M y sid ellinse. 



The genus Lycomysis n. gen., established in this paper on immature male specimens, 

 agrees with two of the subfamilies in possessing a long front process on the labrum, but differs 

 from all other genera hitherto known in having the second joint of the mandibular palps shaped 

 as a saw, in the armature of the telson which has not only a lateral but besides an upper row 

 of spines, and — as far as may be judged from immature specimens — in having the endopod 



I) The genus Arachnomysis Chun is referred to this tribe. The genus Calyptomma Tatt. is omitted, because only immature 

 specimens are known and a judgment on its position is to postporied. 



