190 PLEUROBRANCHID®. 
and of a faience white in front, is marbled behind by irregularly 
disposed interrupted and entangled orange bands. In certain in- 
dividuals some of these bands are a more or less deep brown. The 
edges of the shell, very thin, sharp and lamellose, are of such 
fragility that none of the specimens have it completely intact. 
Japan. 
The substance of Jousseaume’s description is given above. He 
examined four specimens. 
Family PLEUROBRANCHID 2. 
Tectibranchiata Notaspidea in which the gill-plume arises about 
the middle of the right side and extends backward, the dorsal shield 
is fleshy, stiffened by spicules, and either shell-less, or concealing 
wholly or mainly a delicate Haliotiform shell, the radula is multi- 
serial, without rachidian teeth, and the jaws are well developed, com- 
posed of many oblong plates arranged in tessellated pattern ; rhino- 
phores present. 
The group is allied to the Umbraculide, but differs externally in 
the want of a patelliform shell, the posterior gill, etc. It is not 
closely allied to Runeinide, which may be considered a specialized 
and ancient branch of the Notaspidia, divergent in its reduction of 
the radula to a triserial arrangement, and the loss of rhinophores 
by degeneration. 
Pleurobranchide are world-wide in distribution in tropical and 
temperate (rarely in cold) seas. There are many species, especially 
of the genus Pleurobranchus; and the really diagnostic characters 
of a large number of them are not yet known. 
Attention should be directed especially to certain characters, 
which have been very generally neglected, but are essential to any 
thorough systematic knowledge of species of the group. These 
features are the following: (1) Positionsand space-relations of the 
genital orifices. (2) Number of leaflets or plumules of gill, length 
of its adnate and free portions, and smooth or tuberculate nature of 
the rachis. (8) Shape and denticulation of the individual plates 
of the jaws. (4) Denticulation of the teeth of the radula. 
Characters (3) and (4) are readily observed with low powers of 
the microscope; no delicate manipulation being called for. With 
adequate knowledge of the above-mentioned points, and with what 
is already known of the animals, there would be but little difficulty 
in constructing “ keys” or tables for the easy identification of spec- 
