HEMIPENEUS SPINIDORSALIS. 201 
in length, according to the size of the individual, from three fifths to four 
fifths of the length of the rest of the carapace. At its maximum it is equal 
in length to the antennal scale. This remarkable difference between the 
sexes as regards the length of the rostrum is constant in the “ Albatross” 
specimens. 
In the male there is a roundish, shield-shaped disk or plate, pointed 
anteriorly, on the sternum of the antepenultimate thoracic somite, The 
second segment of the posterior thoracic legs is armed with a small tooth on 
the internal side. The inner branch of the first abdominal appendages is re- 
presented by a large membranous petasma, while the proximal segment of the 
inner branch of the second abdominal appendages bears three branches, viz. 
an outer and anterior horny plate, concave within and furnished with sete on 
its distal border, and two inner and posterior branches, one of which has the 
form of a long triangular tooth shorter than the outer plate, the other being 
a longer multiarticulate flagellum, homologous with the inner branch of the 
following pairs of appendages, The sterna of the first three abdominal 
segments are produced into a median tooth between the bases of the 
appendages. 
In the female there is on the posterior part of the thorax a sternal disk 
similar to, but less circular in form than, that of the male, and it is backed 
by an overlapping transverse plate arising from the sternum of the posterior 
thoracic somite. The second segment of the last pair of thoracic legs lacks 
the tooth found in the male. The first pair of abdominal appendages has 
only a rudiment of the internal branch in the shape of a short, slender fila- 
ment. The inner branch of the second pair is similar to the corresponding 
part in the succeeding pairs. The abdominal sterna are toothed as in the 
male. A very large female, with a rostrum as long as the antennal scales, 
from Station 3400, is interesting as showing a tendency to assume a mascu- 
line character in the development of a petasma on each anterior abdominal 
leg. The organ is quite similar in form to the normal petasma of the male, 
only it is much smaller. In other respects this specimen is a normal female 
with well developed genital orifices at the base of the third pair of legs. 
The second and third mavxillipeds are furnished with long exopods. In 
the second maxilliped the exopod exceeds the length of the endopod, while 
in the third maxilliped it attains to the proximal end of the carpus of the 
endopod. The following pairs of thoracic appendages are provided with 
rudimentary exopods. 
