;
or may be wanting. With regard to sense organs the epithelial papillae
of the mantle have been mentioned. There is also in some genera a
median retractile sensory papilla on the dorsal posterior surface
above the rectum, not covered by the cuticle.

_Development_ has only been described in _Myzomenia banyulensis_, by
G. Pruvot. It closely resembles in the early stages that of Chitons.
The external surface of the trochosphere is formed of a number of
ciliated test-cells. The ectoderm behind the ciliated ring develops
spicules, and the post-oral region of the larva elongates. Later the
ciliated ring or velum disappears and seven imbricated calcareous
plates, made up of flattened spicules, are formed on the dorsal
surface. This appears to indicate that the Neomeniomorpha are
descended from _Chiton_-like ancestors, and that they have lost their
shell valves.

_Classification of the_ NEOMENIOMORPHA.--Fam. 1. _Lepidomeniidae._
Slender, tapering behind, with subventral cloacal orifice; thin
cuticle without papillae; flattened spicules; no gills.
_Lepidomenia, Ismenia, Ichthyodes, Stylomenia, Dondersia,
Nematomenia, Myzomenia, M. banyulensis_, Mediterranean and Plymouth.

Fam. 2. _Neomeniidae._ Short, truncate in front and behind; cloacal
orifice transverse; gills present; rather thin cuticle; no radula.
_Neomenia_ (_N. carinata_, N. Atlantic and N. and N.W. Scotland),
_Hemimenia_.

Fam. 3. _Proneomeniidae._ Elongated, cylindrical, rounded at both
ends; thick cuticle with acicular spicules; radula polystichous or
wanting. _Proneomenia, Amphimenia, Echinomenia, Rhopalomenia_ (_R.
aglaopheniae_, Mediterranean and Plymouth), _Notomenia, Pruvotia,
Strophomenia_.

Fam. 4. _Parameniidae._ Short and truncated in front; thick cuticle,
often without papillae; gills and radula present. _Paramenia,
Macellomenia, Pararhopalia, Dinomenia, Cyclomenia, Proparamenia,
Uncimenia, Kruppomenia._

Suborder II. CHAETODERMOMORPHA.--Aplacophora without distinct ventral
groove, with single median unisexual gonad, with differentiated
hepatic sac, and with cloacal chamber furnished with two bipectinate
gills. There are only two genera in this suborder: _Chaetoderma_, and
_Limifossor_ from Alaska. The characters therefore are very uniform.
The body is worm-like and cylindrical, the posterior half a little
thicker than the anterior; t