118 
NATURAL HISTORY. [[EAST. ZOOL. 
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 aperture. 
The family of Worm Shells [ Vermetidce ) 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 
shell is also furnished with a similar slit. Another genus, 
Spiroglyphus , instead of a tube, forms a groove on the sur¬ 
face of other shells, which it covers over and converts into 
a tubular case for its body; in their young state these ani¬ 
mals assume a regular spiral form, but after a time they 
often take another direction. 
The family of Foolscap Limpets (Capulidce) have a 
short conical body, covered with a simple conical shell, 
having a subspiral tip ; they are attached to rocks and other 
marine bodies like Limpets, with which they were formerly 
confounded, but they differ from them in their gills forming 
an oblique line across the back of the neck of the animal; 
their eggs, contained in membranaceous cases, are often 
affixed in radiating groups to the side of the foot. In 
Capulus the foot is flat, with a plaited front edge; in Hip - 
ponyx and Sabia it is, as it were, folded on itself, and is 
unfit for walking upon ; the back of the foot of the former 
of these animals secretes a shelly plate, marked with a 
