564 THE VOYAGE OF H.M.S. CHALLENGED. 



Pleon short, robust. 



First pair of antennae having the flagella unequal ; first joint of the peduncle subequal 

 with the two succeeding ones ; stylocerite prolonged. 



Second pair of antennas having the scaphocerite short, not extending to the 

 extremity of the terminal joint of the peduncle. 



First pair of pereiopoda unequal, larger hand ovate, smooth ; chela short ; dactylos 

 rounded, arcuate, scarcely one-third the length of the palm. The smaller hand robust 

 and more normal in its form. Second pair of pereiopoda slender and multiarticulate, 

 subequal in length with the first pair. 



Length, entire, . . . . . .17 rum. (0 6 in.). 



„ of carapace, 



Depth of carapace, 

 Length of pleon, 

 „ of telson, 



3-5 „ 



9 „ 



9 



Habitat. — Arafura Sea. One specimen ; female. 



Dana records his specimen from the Sooloo Sea at a depth of 6 fathoms, and from 

 the Fiji Islands. 



Betseus, Dana. 

 Beteeus, Dana, U.S. Explor. Exped., Crust., vol. i. p. 558. 



" Like Alplieus in the eyes, antenna? and feet. Front without beak. Anterior 

 hands more or less inverted, the movable finger being the lower and outer." 



Such is Dana's description, but it appears to me to be one more convenient for 

 classificatory purposes than natural in arrangement. 



In the most marked cases the rostrum is a very unimportant feature in this group, 

 and is frequently reduced to a slender point, so that its absence altogether is a character 

 that appears to me to be of secondary importance. Nevertheless it appears to be a 

 very constant law, that an important, but not conspicuous, internal variation may 

 be correlated with a slight but constant external variation in form. 



Dana says that the inverted position of the propodos is also a marked character of 

 the genus, but this appears not to vary much from the condition in some species of 

 Alplieus, as the abnormal form of the propodos in its relation to the dactylos is one of 

 the striking features of many of the species. 



The arrangement of the branchiae is the same as in Alplieus, and so are most of the 

 external parts, but in one specimen, in which the female was gravid with ova, I observed 

 that they differed from those of Alplieus both in form, size, and arrangement. In 

 Alplieus the ova are generally round, small, and massed together, as in most Macrura, 

 by small connecting threads, while in Betams they are larger and more oval. 



