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. 
O 
Antarcturus adareanus. 
(Plate V., fig. 1.) 
Arcturus adareanus Hodgson ( 8 ), pp. 249-250. 
Specific characters :— 
A small spine at the autero-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 
