370 A HISTORY OF RECENT CRUSTACEA 
coalesced. The second antenne are large and long; the 
mandibles have a molar tubercle but no ‘ palp;’ the outer 
plate of the first maxille and the inner plate of the second 
are broad ; the maxillipeds have an oval epipod, a broadly 
expanded plate to the second joint, and the five joints of 
the ‘palp’ not very large; the first four pairs of limbs of the 
pereon are directed forwards, slender, ciliated, with the 
terminal joint minute; the last three pairs are stouter, 
ambulatory, with the terminal joint bifid. The opercular 
uropods have the inner branch much shorter than the 
peduncle, the outer branch rudimentary or sometimes 
entirely wanting. When the valves are closed the branch 
of the uropods which is homclogically the outer is shut up 
inside, even when present. 
Arctirus, Latreille, 1804, has the flagellum of the 
second antenne more than four-jointed, the fourth segment 
of the pereeon not greatly longer than the others, the mar- 
supium of the female composed of four pairs of plates. 
The arctic Arcturus Baffini (Sabine) grows to a length of 
three inches. Mr. F. E. Beddard has described thirteen 
new species brought from various parts of the world by the 
Challenger. Others have been described by Miers, Sars, 
and Studer. Almost all have a striking appearance from 
the armature of spines or tubercles. In their clinging 
habit and general appearance they have some resemblance 
to the amphipod group, the Caprellidze, some of which are 
also very spinose. It is interesting to observe that in 
creatures which are structurally very distinct a similar 
mode of life goes with a similar general appearance, so that 
the similarity of life may be supposed to have produced the 
similarity of look. 
Astacilla, Cordiner, 1795 (=Leacia, Johnston, 1825), has 
the flagellum of the second antennz not more than four- 
jointed, the fourth segment of the pereeon much longer than 
any of the others, and the marsupium of the female con- 
sisting of two plates affixed to this segment. There is no 
reason for discarding Johnston’s Leacia, on the ground that 
the different name Leachia was preoccupied. Itis acommon 
and quite justifiable practice to form generic names by 
