228 MARINE BIOLOGY OF THE SUDANESE RED SEA. 
fig. 2d, he represents the masculine appendix in connexion with a branchial 
plate, and describes the figure as “ L’une des fausses pattes branchiales de la 
premitre paire.’ Von Hbner in 1868, when describing his genus Helleria, 
and comparing it with 7yylos, made it clear, I think, that the masculine 
appendix in both genera belonged to the second pleopods, the missing pair 
being the first. The same author states, I think, correctly that the pleopods 
here, as elsewhere, are double-branched. As he expresses it, “ they carry as 
well the branchial operculum as the branchial sack.” The two, however, 
are here closely superposed. The uropods are bilaminar, the outer, that is, 
the ventral opercular leaf, having apically a small semi-oval setiferous branch, 
regarded as the exopod. Closely applied to the opercular leaf is another, 
which is distinct from it, at least on the upper and lower borders, reaching 
about level with it at the narrowed setulose apex, but not reaching its top 
with its strongly rounded upper border. 
The species which I now propose to add to the genus is distinguished 
not only by its very small size but by its relative narrowness, suggestive 
rather of the genus Stenoniseus, Dollfus, than of Zylos. The maxillipeds 
are six-jointed, having the palp, therefore, three-jointed instead of two- 
jointed, ax given by Budde-Lund in the family character. Y 
oung ones, of 
the same length, of 7ylos latreillii, Audouin, brought to me from Formiae 
by the late E. Mello Saunders, Bsq., are globose, half as broad as long, and 
in two of them that were dissected no trace appeared of the male appendix. 
The solitary specimen in Mr. Crossland’s collection accordingly seems to 
represent a new species, in proximity to T. albidus, Budde-Lund. 
TYLOS EXIGUUS, sp.n. (Plate 23.) 
The small size of the specimen leaves it open to the suspicion that it may 
be the young of some species already known. Against this explanation 
may be set the development of the second pleopods with male characteristics, 
and the general shape, which is not a full oval as usual in the genus, but 
of such narrowness as to make perfect globation not very feasible. As 
will be seen from the figures, the other details agree closely with the 
corresponding parts of 7. latreilli. 
It belongs to the group of species in which the scutellum, surmounting 
the epistome, is conspicuously triangular, not as in 7. granulatus, Krauss, 
quadrate with rounded upper margin. In the last-mentioned species the 
triangular apex is bent so as to be quite inconspicuous. 
~The second antenne have the fifth joint of the peduncle scarcely as long 
as the flagellum, of which the first two joints are equal in length, each 
considerably longer than the tapering third joint. In 7. albidus the third 
joint is described as the longest. 
The mandibles show five or six plumose setee, two separate groups between 
the cutting-edges and the molar, and a large one by itself on the further side 
