638 ON CRUSTACEA BROUGHT BY DR WILLEY FROM THE SOUTH SEAS. 



peraeon segments of the female are much narrower and, except the first, much longer 

 than those of the male. Of Alcirona insulari^ he had at command three specimens, 

 but these comprised no female, were not fully grown males, and were not all exactly 

 alike. They ranged in size from 3'7 to o"l mm., the longer ones having more joints 

 iu the antenual flagella, the telson distally more narrowed, and a greater hirsuteness 

 on the hinder half of the body. The shajje is likened to that of Cirolana parva, so 

 that these joung males, as also the figure shows, are in agreement with the male of 

 Alcirona krebsii in general appearance. 



Two specimens were obtained by Dr Willey which do not seem easily separable 

 from Hansen's insiilaris. The}' are a male and a female, both adult, the former about 

 5 mm., the latter about 4 mm., in length. But the singular thing is that here it is 

 the male which has the segments of the peraeon much narrower and longer than 

 those of the female, just the reverse of what is found in Alcirona krebsii, and this 

 singularity remains whether the identification of the specimens with Hansen's species 

 be valid or not. There are certain differences to be noted, but these may well be 

 attributed to the maturity of the specimen. 



The male differs from the female not only in the proportions of the peraeon, 

 but also in the pleon, the penultimate segment of which has a small projecting tubercle 

 in the middle of the hind margin while the triangular terminal segment is distally 

 very narrow, its serrate sides and spinulose truncate point being girt with plumose 

 setae. Down the centre there is a low ridge. On the seventh joint of the first 

 guathopod the four teeth are less erect than in Hansen's figure, lying in the direction 

 of the nail and being successively larger. Those of the second guathopod are a little 

 smaller but have otherwise the same character. Also in both gnathopods there are 

 six or seven little nodular teeth fringing the inner margin of the sixth joint. The 

 spines of the fourth joint in the gnathopods and also in the first peraeopods are very 

 stout. The second pair of pleopods are just like those figured by Hansen for the male 

 of Alcirona krebsii. 



The female specimen had the marsupium filled with twelve large oval hardened 

 eggs, two of them brown, the rest pale. The general habit was like that of the young 

 male, but with the telson distally more narrowed than in Hansen's figures. The first 

 antennae have the first joint thickened at the base, much shorter than the second, the 

 thu'd joint in one antenna equal to the first joint of the five-jointed flagellum, in the 

 other antenna shorter than that joint. The second antennae in both sexes have 20 — 21 

 joints in the flagellum. In the maxillipeds of the female the broad vibratory lamina of 

 the second joint reaches slightly beyond the rather narrow palp. In the gnathopods the 

 seventh joint has two minute teeth followed by a longer one adjoining the nail, much 

 like the formation in the first peraeopods of the male. In the female all the peraeopods 

 have the finger with its margin simple except for a prominence at the base of the nail. 



Habitat. Blanche Bay, New Britain, 1.5 — 20 fathoms. 



^ga niultidigita, Dana, 6'3 mm. long, from Balabac Passage, north of Borneo, is 

 certainly an Alcirona, and may possibly be identical with the present species. In the 

 terminal segment it agrees fairly with the account of the male pleon above given, but 

 the size and shape of the body differ ; the proportions of the first antennae, and the 



