370 A HISTORY OF RECENT CRUSTACEA 



coalesced. The second antenna are large and long ; the 

 mandibles have a molar tubercle but no ' palp ; ' the outer 

 plate of the first maxillae 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 

 perseon 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, theT 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. 



Arcturvs, Latreille, 1804, has the flagellum of the 

 second antennse more than four-jointed, the fourth segment 

 of the perseon not greatly longer than the others, the mar- 

 supium of the female composed of four pairs of plates. 

 The arctic Arcturus Bajfini (Sabine) grows to a length of 

 three inches. Mr. P. 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 Caprellidse, 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, Gordiner, 1795 (=Leacia, Johnston, 1825), has 

 the flagellum of the second antennae not more than four- 

 jointed, thefourth segment of the peraeon much longer than 

 any of the others, and the marsupium of the female con- 

 sisting of two plates afiixed to this segment. There is no 

 reason for discarding Johnston's Leacia, on the ground that 

 the different name Leachia was preoccupied. It is a common 

 and quite justifiable practice to form generic names by 



