93 
EAST. ZCOL. GAL.] NATURAL HISTORY. 
The family of Pyramid Shells ( Vyramidellidce , Case 21) 
are at once known by the oblique plaits on the front of 
the pillar lip of the polished, spotted, turreted shell, and 
by their tentacles being broad and folded like the ears 
of a hare; they have the eyes at the inner side of 
their base, like the Auriculce; their operculum is horny, 
with a flap on the inner side to adapt it to the plaits on 
the pillar. 
The family of Turned Shells ( Tornatellidce , Case 21) 
also have plaits on the pillar, and a horny operculum 
with a flap ; but the animal has no true tentacles, only an 
expanded disk on the front of the body, somewhat like 
the disk of the Bulladce. 
2. The animals of the families which follow have their 
gills formed of long filaments, and often exserted when the 
animal is expanded; their shells are very variable and 
anomalous in form, and often have a very large aper¬ 
ture. 
The family of Valve Shells ( Valvatidce , Case 21) are 
small fluviatile Mollusca, found in rivulets, with an or¬ 
bicular many-whorled spiral operculum ; they are remark¬ 
able for having their gills, which are formed of long 
spiral plates, protruded on the outer side of their base 
beyond the shell when they walk. The shells are re¬ 
gular spiral, with a round simple mantle, and covered 
with a pale olive periostraca. 
The family of Worm Shells ( Vermetidce , Case 21) are 
peculiar for having an irregularly tubular shell, which is 
generally attached, by its outer surface, to shells and other 
marine bodies. The body is elongate, and living thus fixed, 
the foot is not furnished with a distinct disk for walking; 
its two ends are folded together, and its hinder end is pro¬ 
duced into a flat orbicular disk, as large as the mouth of 
the shell, which is generally protected by an orbicular 
horny operculum. The operculum is very variable in form ; 
it is sometimes concave, with a central star, at others it is 
formed of many whorls with a thin raised outer edge, and in 
Siliquaria , after the animal has arrived at its full size, it 
continues to form new whorls to the operculum, which are 
nearly all of the size of the mouth of the shell. This lat¬ 
ter genus is also peculiar for the mantle having a slit near 
the edge of the gill, as in the Haliotides , and its tubular 
