294 



its maximum width, and the structure of its distal part subject to notable 

 age and individual variation. Usually, adult individuals have a completely 

 segmented extremity in which the distal part comprises five segments, 

 the last being finger-shaped; however, individuals ha><e been encountered 

 in which pereopods VII are asymmetrically developed with respect to 

 shape and general segmentation; crustaceans have also been found with 

 a three- and four- segmented distal part or with complete segmentation of 

 the extremity, but with a bud-shaped (or gemma-shaped) 7th segment. 



The pleon is longer than the pereon. The urosome is shorter than 

 somite III of the pleon. Urosomite I is slightly shorter than the last 

 (geminate) urosomite; the border between the fused urosomites II and 

 III is demarcated by a sharp projection and lateral notches. The distal 

 angles of the urosome protrude backward. The basipodite of uropods I 

 is equal to the rami in length, distally broadened, with a sharply pro- 

 jecting inner margin; the rami are distally unevenly denticulate, prox- 

 imally on the outer side finely denticulate, on the inner side smooth; 

 the endopodite is slightly longer than the exopodite. The basipodite of 

 uropods II is notably shorter than the rami and hardly extends beyond 

 the end of the urosome; the endopodite is longer than the exopodite and 

 in females slightly, but in males distinctly broader than the exopodite; 

 the exopodite is very finely denticulate on the inner margin and more 

 coarsely on the outer; the endopodite is slightly denticulate on the outer 

 margin and smooth on the inner except for three-four subapical denti- 

 cles; the rami are narrower and more distinctly denticulate in the female. 

 The basipodite of uropods III is 2.5 times longer than the rami; the 

 rami are equal in length, the endopodite barely broader; the exopodite 

 is finely denticulate on the outer margin except in the proximal part, 

 and also on the inner margin except distally where minute denticles 

 are interspersed among much larger ones; the endopodite is finely den- 

 ticulate on both sides but sometimes the fine denticulation is inter- 

 rupted by large denticles. The poorly expressed sexual dimorphism in 

 the structure of uropods II of Cyllopus is a characteristic difference from 

 the genus Vibilia in which of the same type dimorphism is observed 

 in the structure of uropods III. The telson is small, semicircular or 

 roundish-triangular, its length less than its basal width and half the length 

 of the last urosomite. 



Distribution: Circum-antarctic, reaching the higher latitudes and 

 sometimes forming small concentrations, often with Parathemisto 

 gaudichaudi. 



242 2. Cyllopus lucasi Bate, 1862 (Fig. 120) 



Bate, 1862: 306; Bovallius, 1889: 16; Barnard, 1930: 409.— antarc- 

 ticus Spandl, 1927: 175. 



Large crustaceans, reaching up to 23 mm in length. 



