234 W. M. Tattersali. : Two new Mysidce. [Voiv. II, 



the male, appears to be simple and rudimentary as in the female, 

 the genus thus agreeing in this respect with Neomysis and Diamysis. 

 The species here dealt with is otherwise so closely in agreement 

 with the general characters of Potamomysis pengoi that for the pres- 

 ent I prefer to refer it to the same genus, which may therefore be 

 diagnosed as follows : — 



Potamomysis, Czerniavsky. 



Antennal scale long and narrow, subulate, ciliated all round, 

 two jointed. 



Thoracic legs with the tarsus three to four jointed. 



Telson short ; apex entire, truncated, armed with numerous 

 spines ; lateral margins armed with short subequal spines along 

 their entire length ; no median apical setae. 



P/go/>o^s of the male ; the first, second, third and fifth pairs 

 simple, uniramous and rudimentary as in the female ; the fourth 

 pair with a short peduncle and inner ramus as is usual in the sub- 

 family MysincB, the outer ramus very long and slender, three 

 jointed, the terminal joint bearing two long spiniform ciliated fila- 

 ments and a single long smooth filament. 



The genus is thus very closely allied to both Neomysis and 

 Diamysis, but the form of the telson suffices to distinguish it from 

 both, while male specimens are further distinguished by the form 

 and armature of the fourth pair of pleopods. 



Potamomysis assimilis, sp. nov. 



(Plate xxi, figs i — 8.) 



General form (fig. i) small, linear and compact. 



Carapace (fig. i) covering all the thoracic segments but the last ; 

 only slightly produced in front into a small obtuse rostral projec- 

 tion ; antero-lateral corners apparently rounded. 



Pleon (fig. i) longer than the thorax; first five segments more 

 or less subequal in length ; sixth segment one-and-a-half times as 

 long as the fifth. 



Antennular peduncle (fig. 2) about half as long as the antennal 

 scale; basal joint the longest; second joint small; third joint 

 longer than the second and more robust, with a single plumose seta 

 at the inner distal corner ; a similar seta at the inner distal corner 

 of the second joint, and at the outer distal corner of the third 

 joint. 



Antennal peduncle (fig. 3) less than half as long as the scale, 

 with the terminal two joints subequal in length. 



Antennal scale (fig. 3) equal in length to the last two segments 

 of the pleon, long and narrow, subulate in shape, about seven 

 times as long as broad, setose all round, two jointed, the second 

 joint equal to between one fourth and one fifth of the entire length 

 of the scale ; spine on the outer corner of the basal joint well- 

 developed and acute. 



