48 CLASS GASTEROPODA. 
amati, Delle Chiaie. Memor. pl. ii. f. 1—8; a small animal, 
an inch long and two broad, when the wings are extended. 
GASTROPLAX, Blain. UMBRELLA, Lam. 
Until the anatomy of this singular genus be more closely 
studied, we must place it in the order tectibranchiata, and 
even near pleurobranchus. The animal is large and circular, 
the foot projects considerably beyond the mantle, and its 
upper surface is studded with tubercles; the viscera are in a 
round, superior, and central part; the mantle is visible only 
by its slightly projecting and trenchant edges along the whole 
of the front and of the right side; the lamellated pyramidal 
gills, like those of pleurobranchus, are under this slight 
margin, and behind them is a tubular anus. Under this same 
margin, and forwards, are two tentacula, longitudinally cleft, 
still as in pleurobranchus; and at their internal base are the 
eyes: between them is a sort of proboscis, which perhaps is 
the organ of generation. ‘There is a large concave space in 
the anterior margin of the foot, the edges of which can be 
drawn up like a purse, and at the bottom of which is a tubercle 
pierced by an orifice, which perhaps is the mouth, and sur- 
mounted by a fringed membrane. The inferior surface of the 
foot is smooth, and serves the animal to crawl on, as in the 
other gasteropoda. 
The shell is strong, flat, and irregularly rounded, thickest in 
the middle, with trenchant edges, and marked with slightly 
concentric strie. It was at first thought to be attached to the 
foot, but more recent observation has proved that it is on the 
mantle, and in the usual place. 
In the specimen from the British Museum, described by M. 
de Blainville, under the name of GASTROPLAX, the shell is 
in fact attached to the under part of the foot, and it is difficult 
to determine by what means; the mantle is, however, so thin, 
that it seems as if it must have been protected by the shell. 
