60 PERCY SLADEN TRUST EXPEDITION 
considerably longer than is indicated in his figure. I believe, none the less, that the 
specimens may safely be referred to the same species: the presence of the spinules on the 
inferior margin of the last abdominal somite in the male appears to constitute a valid 
specific criterion. 
Lucifer typus, auct., as typified by a number of specimens from the Ceylon coast, 
is very closely allied to this species; but males may easily be distinguished from it 
by the invariable absence of the pair of spinules behind the posterior tooth on the ventral 
edge of the last abdominal somite. Both sexes differ from Dana's L. reynaudw in the 
proportions of the outer uropod. These segments are broader in L. typus, not more than 
four and a quarter times as long as wide, and the spime which terminates the outer 
margin does not reach so far backwards. 
Family Peneide. 
GENNADAS, Spence Bate. 
Considerable difficulties are encountered in the determination of the species of 
Gennadas, and this seems more especially to be the case with the several closely allied 
forms occurring in the Indian Ocean, the Bay of Bengal and the Arabian Sea. The 
species found in these waters are, for the most part, very closely allied, and the sexual 
characters are almost the only features of diagnostic value. These characters are, indeed, 
well defined, and their use renders the recognition of any species which has been 
adequately figured a comparatively simple matter: the difficulty lies in recognising the 
two sexes of a single species. Gennadas parvus, Bate, and G. sordidus, Kemp, afford an 
instance of this. Both species have been described from the male sex only, and though 
the petasmata yield distinctions of a quite obvious nature, in other respects the characters 
of the two are so closely similar that very little reliance can be placed upon them for 
specific determination. In examining Mr Stanley Gardiner’s collection several females 
were found which must certainly be referred to one of these two species, while others 
which must also be identified with one of the two forms, but have a different type of 
thelycum, are included in a fine collection of Gennadas recently made in Indian waters 
by the R.I.M.S.S. “Investigator.” On consideration, I have decided that Mr Gardiner’s 
specimens represent the female of G. parvus, while those obtained by the “ Investigator ” 
are females of G. sordidus. In making these determinations I have, however, been 
largely influenced by the fact that males of G. parvus, which are very scarce in the 
“Investigator” material, are found to the exclusion of male examples of G. sordidus 
in Mr Gardiner’s collection. The conclusions, therefore, are not based on evidence of 
a really satisfactory nature and, should further investigations reveal the existence of a 
third form of male exhibiting the same affinities in general structure that exist between 
G. parvus and G. sordidus, the matter will be still further complicated. 
6. Gennadas parvus, Spence Bate (Plate 7, figs. 6, 7). 
Gennadas parvus, Kemp, Proc. Zool. Soc., 1909, p. 721, pl. 83, figs. 1—6, pl. 75, fig. 1. 
Sept. 27, 1905. S. by E. of Farquhar, 10° 27’S., 51° 17’ EK. p, 800—0 fms. ; one 
female. gq. 1000 to 0 fms. ; one male and four females. gs. 750 to 500 fms. ; two females. 
