9492 PROCEEDINGS OF THE NATIO NAL MUSEUM. VOL. XXXIV. 
Genus ORCHESTOIDEA Nicolet. 
1849. Orchestoidea NIcoLET, in Gay, Hist. Chile, III, p. 229. 
1906. Orchestoidea STEBBING, Das Tierreich, Lief. 21, p. 527. 
This genus agrees with both sexes of Zalitrus and with the female - 
of Talorchestia in having the first gnathopod simple, differing from 
the male of Zalorchestia and both sexes of Orchestia in which the first 
gnathopod is subchelate. All the four genera have the second gnatho-- 
pod in the female feebly chelate, but in the male this is the. case 
only with Zalitrus, the second gnathopod of the male in the other 
three genera being powerfully developed. These distinctions do not 
enable us to separate a species of Zalorchestia or Orchestoidea from 
one of Zalitrus, when only female, nor yet an Orchestia from a 
Talorchestia, when only male specimens are available. But as these 
animals are generally plentiful, where they occur at all, any difh- 
culty arising from the absence of one or other sex will not as a rule 
be of long standing under the energy of modern research. 
ORCHESTOIDEA BIOLLEYI, new species. 
Plate XII. 
Integument smooth and shining, but under a igh power showing 
the three-spiked markings often seen in this family. Fifth side-plate 
of person as deep as fourth. Postero-lateral corners of third pleon 
segment quadrate with minute projecting point. : 
Eyes large, dark, roughly rounded, in the largest specimens sep-- 
arated only by a short space at the top of the head. 
First antenne very short, third joint of peduncle rather the longest, 
equal to the little five-jointed flagellum. Second antenne in the male 
longer than the body, last joint of peduncle considerably longer than 
the preceding joint, flagellum 39-jointed, more than thrice as long 
as the peduncle; in the. Roane much shorter than the body, flagellum 
23-jointed, not greatly longer than the peduncle. 
The mouth-organs are in close agreement with those of Valitrus 
and Talorchestia. The minute palp of the first maxille appears to 
be 2-jointed, with the second joint considerably shorter than the 
first. 
The first sanihooode in accord with the generic character, are 
simple in both sexes, but in the male the rather large fifth joint has 
at the distal end of the hind margin a transparent bulb or bubble- 
like expansion, which is wanting in the female. 
The second gnathopods of he male have the fifth jomt very 
small and feebly separated from the strong ovoid sixth joint, the 
hind margin of which is characterized by having near the distal end 
a small .transparent bulb, the distal end itself being rounded and 
tipped with a spine. Within this apex the strong finger closes into a 
