ISOPODA. 



35 



absence of cephalic horns, may be found which will assist in further dividing the 

 original genus ; but, unless these divisions are indicated by some prefix to the name 

 Arcturus so as to show what has become of closely related forms, no advantage can 

 accrue to zoological nomenclature. 



ANTARCTURUS ADAREANUS. 



(Plate V., fig. 1.) 



Arcturus adareanus Hodgson (8), pp. 249-250. 



Specific characters : 



A small spine at the antero-lateral angle of the cephalosome, and a pair of stout spines behind 

 the cephalic horns. 



Two dorso-lateral spines on the first segment of the mesosome. 



This species is very closely allied to A. glacialis Beddard, but may be readily 

 distinguished from it by the characters given above, and especially by the first named. 



The cephalosome has its anterior margin incurved as usual, and its antero-lateral 

 angle terminates in a spine ; a minute spine occurs behind this and in front of the 

 eyes. The cephalic horns are not very large, they lie between the eyes and arch 

 slightly outwards. A short distance behind them is another pair of small spines. The 

 cephalosome is otherwise smooth. 



The mesosome is covered with small spines throughout. The first four segments 

 progressively increase in length to a slight extent. The posterior margin of each 

 segment consists of a transverse ridge, which, in the case of the first three, widens out 

 laterally to the full length of the segment. The dorsal area in front of the ridges is 

 occupied by two more or less distinct rows of spines. The ridge on the first segment 

 also bears two stout but blunt spines dorso-laterally, and the posterior border of the 

 two following segments at least has a distinct row of small spines, laterally the 

 segments are covered with several small blunt spines. The fourth segment is 

 similarly covered, but here the lateral area is distinct from the transverse ridge. The 

 three posterior segments progressively decrease slightly in length ; each has a raised 

 transverse spinous ridge, which, in the case of the first, widens out laterally, both 

 anteriorly and posteriorly ; in the case of the other two the ridges are straight 

 anteriorly and widen posteriorly. Small blunt spines are numerous. Laterally the 

 epimera form prominent swellings over "the base of their respective appendages and are 

 more or less well supplied with small spines. 



The first three segments of the metasome are distinct though fused and covered 

 with the same small spines. The epimera are comparatively large, roughly ovate 

 structures, decreasing in size from the first to the third. The urosome is rounded, and 

 at its extremity bears two prominent straight spurs. Its surface is covered with small 

 spines which are seen to be in rows. A median row of small spines, a row of larger 

 ones on either side and two other rows less distinct. The uropoda are large, the basal 



M 2 



