| | | |3-4
| | | | | | | |7-8

|_I. quadrivalvis_,
| |32-33
| | |--
| | | |10
| | | | |8
| | | | | |5
| | | | | | |4
| | | | | | | |8

SCALPELLUM: disc _hoof-like_, generally _pointed_ and elongated, with a
single spine on the hinder margin; end segment, with a notch on the
inner[61] side, bearing two spines, longer than on the exterior corner.

|_S. vulgare_,
| |39
| | |19
| | | |10
| | | | |10-11
| | | | | |5-6
| | | | | | |6
| | | | | | | |7

|_S. ornatum_,
| |36
| | |21
| | | |10
| | | | |12
| | | | | |--
| | | | | | |--
| | | | | | | |--

|_S. Peronii_,
| |30
| | |19
| | | |--
| | | | |9
| | | | | |6
| | | | | | |5
| | | | | | | |10

POLLICIPES: disc small, _hoof-like_, not pointed, with a single spine on
the hinder margin; end segment, as in _Scalpellum_.

|_P. cornucopia_,
| |20
| | |--
| | | |6
| | | | |6
| | | | | |6
| | | | | | |6
| | | | | | | |8

[61] In the diameter of the disc, the thin membranous border,
which is present in the first three genera, is included; but I
have some doubts, whether this border be not the first rim of
cementing tissue, as all the specimens, of which measurements are
here given, had been removed after attachment. In using the terms
inner and outer sides of the end segment, it is supposed, that
this segment is stretched straight forwards, instead of being
bent rectangularly outwards, as in its natural position; and then
there can be no doubt which is the inner and outer sides.

It should be observed that the evidence in this summary is of a
cumulative nature. If we think it highly, or in some degree
probable,--from the ordinary form of _Ibla Cumingii_ having been shown
on good evidence to be exclusively female,--from the absence o