ISOPODA. 29 



in the adults and the eight-jointed first antennae. In the limbs the nail is rather 

 more distinct from the trunk of the finger than it is in the full-grown animal. The 

 seventh segment of the person is, as usual, without limbs, and resembling the 

 segments of the pleon which at this stage are much narrower than the perseon. The 

 telsonic segment shows a broadly rounded or very obtusely-angled apical margin, which 

 like those of the uropods, and possibly also those of the pleopods, is feebly and 

 microscopically fringed with setules. There is no subapical constriction of the telsonic 

 segment as in the " pullus stadii primi" of Irona foveolata, and the inner branch of 

 the uropod is broader than in the young of that species. 



In Irona nana, Schiodte and Meinert, the adult female has the outer branch of 

 the uropod much longer than the inner ; in Hansen's species the inner is considerably 

 longer than the outer, so that both species may be easily distinguished from the one 

 here described. 



Family: SPHyEROMIDyE. 



The genera that with more or less acceptance have maintained places in this family 

 are Sphoerorna, Bosc, 1802; Campecopea, Leach, 1813; Cymodoce, Leach, 1814; 

 Dyaamene, Leach, 1814 ; Ncesa, Leach, 1815 (for Nescea, Leach, 1813, preoccupied) ; 

 Ciliccea, Leach, 1818; Zazara, Leach, 1818; Cerceis. Amphoroidea, Cassidina 

 Ancinus, all four instituted by Milne-Edwards in 1840; Monolistra, Gerstaecker 

 1856; Isocladus, Miers, 1876; Ceratocephalus, Woodward, 1877 (not preoccupied 

 by Ceratocephala, Warder, 1838, and therefore taking precedence of Bregmocerella 

 Haswell, 1885); Cycloidura, Stebbing, 1878 (for Cyclura, Stebbing, 1874, 

 preoccupied); Scutidoidea, Chilton, 1882; Plakarthrium, Chilton, 1883 (of which 

 Chelonidium, Pfeffer, 1887, is a synonym, so that the family Chelonidiidas if 

 maintained must be named Plakarthriidee) ; Haswellia, Miers, 1884 (for Calyptura, 

 Haswell, 1881, preoccupied); CymodoceUa, Pfeffer, 1887; No?sicopea, Stebbing 

 1893; Ccecosphceroma, Dollfus, 1896 (part); Tecticeps, H. Richardson, 1897 

 Exosphceroma, Stebbing, 1900; CassidineUa, Whitelegge, 1901; Chitonopsis, 

 Whitelegge, 1902; Parasphceroma, Stebbing, 1902; Vireia, Dollfus, 1905. 



This rather unwieldy group suffers at present under various difficulties, towards the 

 solution of which only a few suggestions can here be volunteered. Eugene Hesse in 

 1872 undertook to prove, with a reserve which he evidently scarcely entertained that 

 Sphceroma represented the female of Cymodoce and Dyaamene the female of Ncesa. 

 The discovery of undoubted males in several species of Sphceroma has shown that the 

 first part of his hypothesis is untenable, but for the second part there is much to be 

 said. It is exceedingly probable that Dynamene montagui, Leach, is the young male 

 and that Dynamene rubra and viridis, Leach, are young forms, female or male of 

 Ncesa bidentata (Adams), which is the adult male. The colouring, the general 

 structure, and very frequent occurrence under similar conditions of these four forms 

 give warrant to this belief (see ' Journ. Linn. Soc.,' London, vol. 12, p. 148, 1874). 

 From acceptance of this view will follow the necessity of cancelling one of the generic 



