ringed structure,
but is not fibrous; the contents in the best specimen consisted of a
mass of spermatozoa, which I saw with perfect distinctness. The testes
are unusually large and egg-shaped.

_Ova_, spherical, 5/400ths of an inch in diameter, united as usual into
two ovigerous lamellae. The ovigerous fraena are extraordinarily small,
and might be very easily overlooked; their length, in a full-sized
specimen, was only 7/400ths of an inch, and they projected only 2/400ths
from the inner surface of the sack. The glands on their margin, to which
the lamellae adhere, are pointed oval, with an extremely short footstalk,
and that rather thick; the entire length of gland and footstalk, being
only 2/3000ths of an inch. The larvae, in their first stage of
development, offer the usual characters, and closely resemble those of
Scalpellum; the probosciformed mouth, however, is remarkably prominent,
and the limbs unusually thick.

_Affinities._--This species most closely resembles _I. Cumingii_, and
cannot be distinguished externally, except by the absence of the blue
colour on the marginal and interior portions of the valves; and this can
hardly be ascertained without separating and cleaning them, owing to the
blueness of the underlying corium. Internally some slight differences
may be perceived in the form of the valves. Considering these so slight
differences, it is highly remarkable that this species should be
hermaphrodite, whilst _I. Cumingii_ is unisexual. There is a greater,
though still slight, difference in the included animal's body; the palpi
in _I. quadrivalvis_ are blunter, the mandibles smoother, the olfactory
orifices darker-coloured; the rami of the first cirrus more unequal, the
spines more numerous on the segments of the posterior cirri, and lastly
and most conspicuously, the caudal appendages are very much longer
relatively to the length of the sixth cirrus, than in _Ibla Cumingii_.

COMPLEMENTAL MALE.

I have examined one specimen of the hermaphrodite _I. quadrivalvis_,
preserved in spirits from Kangaroo Island, and one dry from Adelaide,
both places in South Australia, and four from an unknown locality,
purchased from Mr. Sowerby; and within five out of these six specimens,
males were attached. In one of them, two males of different ages were
included, one adhering to the peduncle of the other: in _I. Cumingii_,
also, it may be remembered, there was a case of two males parasitic on
one female. I may a