EEPORT ON THE ISOPODA. 9 



ill leiigtli those of many Cymotlioadse ; where the epimera are only moderately developed 

 they are in close contact for the greater part of their length, the anterior slightly over- 

 lapjjing the posterior ; in Sewlis necBva, Serolis hromleijana, and Serolis gracilis the 

 epimera are quite independent for the greater part of their length, and are only in actual 

 contact for a short space close to the junction of the epimera and tergum ; at this point 

 the anterior margin of the epimeron projects forwards as a short rounded process which 

 is received into a "glenoid" cavity between two similar processes, one dorsal and one 

 ventral, of the epimeron in front ; of these processes only traces exist in Serolis scliythei 

 and those species in which the epimera are closely applied to each other ; an intermediate 

 condition is seen in Serolis paradoxa and other species, where each epimeron has two 

 articular processes, one anterior and one posterior ; the anterior process of each segment 

 overlaps the posterior process of the segment in front. 



The epimera of the first three free thoracic segments are invarialjly separated from 

 their terga by a distinct suture ; in some species {Serolis scliythei) the following pair of 

 epimera are also thus separated ; in Serolis latifrons all the free thoracic segments have 

 the epimera divided by a suture from the terga. 



The abdomen in Seivlis consists of three freely movable segments and a terminal 

 caudal shield which represents the three posterior appendages of the abdomen together 

 with the telson. 



The anterior segment of the abdomen is enclosed between the penultimate thoracic 

 and the second abdominal segment, and in one species only has any traces of epimera ; 

 in Serolis latifrons a minute portion is separated otf from the median portion on either 

 side by a suture ; and as this suture is quite continuous with those in front which separate 

 the teroa and sterna of the thoracic segments, it seems that the minute nodule on either side 

 of the first abdominal segment really represents its epimeron. The two succeeding 

 segments are always furnished with epimera, which are, however, never se^iarated by a 

 suture from the terga, and in most cases are short and not prolonged beyond the lateral 

 margin of the caudal shield ; in some species, notably in Serolis hromleyana, the epimera 

 of these segments ai'e elongated, and reach midway down the margin of the caudal shield, 

 or even considerably beyond its termination. 



The remaining abdominal seomeuts are fused with the telson to form a caudal shield 

 which is commonly more or less pentagonal in outline, and is always furnished with a 

 longitudinal carina and sometimes wth a pair of lateral carinas which appear to mark the 

 line of di\dsion between the posterior abdominal segment and the telson ; the greater 

 portion of the caudal shield is occupied by the latter. 



Appendages. — The two pairs of antennce are generally subequal in size, sometimes 

 {e.g., Serolis minuta) the anterior pair, sometimes {e.g., Serolis cornuta) the posterior pair 

 are the longer. 



The anterior antennae consist of four joints and a terminal filament, while the posterior 



(ZOOL. CHALL. EXP. — PART XX5III.— 1 884.) Kk 2 



