22 NATURAL HISTORY. [EAST. ZOOL, 
secretes a shelly plate, which has been compared to the second valve 
of bivalves; as Calyptrccadce , Capulidce, Vanicoroidce. 
Table 20. The family Vermetidce , which have a cylindrical trun¬ 
cated clavate foot not fitted for crawling. They have a horny circular 
operculum. The shell is tubular, irregular, attached by its outer sur¬ 
face to marine bodies, or twisted together in masses. 
Tables 19, 20. The two families which have the foot compressed 
for leaping and unfit for crawling; they are furnished with an oper¬ 
culum, as the Strombs ( Strombidce ), which have an elongated shell 
with an elongated mouth and an expanded outer lip, and the Carrier 
Shells (Phoridce), which have a top-shaped shell, with a square aperture. 
These shells often have the peculiarity of attaching to the outer sur¬ 
face, as it enlarges in size, stones, fragments of other shells, coral, and 
other marine substances, from whence it has been called respec¬ 
tively the “ Conchologist,” and the “ Mineralogist,” as shell or mineral 
preponderated. Some of the species have this habit only in an early 
stage, others retain it during the whole period of their existence; 
some have the margin of the whorls expanded into a broad disk, 
others have this part furnished with a series of long tubular processes 
like the rays of the sun—hence the name of Sun Carriers. The shells 
of the Atlantidce and Pterotracheidce, which are peculiar for having 
an erect compressed fin on the under side of the body in place of a 
foot, with a small orbicular disk for attaching themselves to floating 
objects on its back edge. They live on the surface of the ocean. 
Tables 21—24. The shells of the Scutibranchous Mollusca, the 
gills of which consist of lamellae, forming one or two series on the 
back of the neck or on the under edge of the mantle round the foot. 
They are hermaphrodite. 
Tables 21, 22 contain those which have the eye on a pedicle sepa¬ 
rate from the tentacles, the shells and operculum spiral; the teeth in 
numerous series on the lingual band, the lateral teeth being uniform 
and very numerous and crowded, as the family Turbinidce, Liotidce, 
Trochidce, Stomatellidce , Haliotidce, Fissurellidce , which have the 
sides of the body, above the foot, ornamented with a continuous fringe 
with some beards on its surface, and the shell almost always pearly 
within. The Neritidce have no lateral fringe or beards, and a porcel- 
lanous shell. 
Tables 23, 24. The other families of this Order which have sessile 
eyes, the teeth in a moderate number of series, the outer teeth being 
flat and uniform, as Dentaliadce, Tecturidce, Lepetidcz , Gadinidce, 
Patellidce, which have simple conical symmetrical shells, and Chito - 
nidce, which have a series of eight shelly valves placed in a longitudinal 
series down the back of the animal. 
Tables 25—30 contain the shells of the Heterobranchous Gastero - 
pods, which have variously formed respiratory organs. They are her¬ 
maphrodite, and furnished with spiral or sub-spiral shells. 
Table 25. The shells of the Pleurobranchous Mollusca , where the 
gills form a tuft on the side, under a fold in the mantle, as the families 
Philinidce, JBullinidce , Bulladoc, Amplustradce or Bubble shells, Aply- 
siadce or Sea Hares, Lophicercidce } Pleurobranchidce, and some dried 
