II. Bivalves with the edges of the mantle 
partly connected, and with tube-like 
siphons. 
Plate XXI. fig. a. JZ7tdacna gigas, the Clam, 
is the largest shell known. The large ridged shell 
with undulating edges occasionally attains a length 
of four or five feet. and is sometimes placed in a 
church as a font. The impressions of the two large 
clasp-mussels are close together. The animal inhabits 
the Indian Ocean, and develops a byssus. 
Plate XXII (left side). 
The Cockles have a heart-shaped shell with 
strong marginal teeth. The animal project its foot, 
which is angulated, and ends in a point, through a 
crevice, and uses it for digging and leaping. In 
some places it is an important article of food. There 
are several! closely allied species, and we have figured 
Cardium costatum (fig. b). 
Fig. c. Cyclas cornea is a fresh-water mollusc 
which sometimes burrows and sometimes climbs 
among the water-plants. It has a convex horn- 
coloured shell and two clasp-mussels. 

54 
Fig. d. Tellina virgata has an oval shell 
rounded in front, and the hinder end is somewhat 
folded over. 
Fig. e. Venus verrucosa belong to a large 
genus which is much admired for its elegant oval 
form and strong marginal teeth. The species 
figured inhabits the Mediterranean, 
Fig. f. The Razor-Shell (Solex vagina) is open 
at both ends. The animals burrow one or two feet 
deep in the sand and mud, and are sometimes eaten, 
but are not much esteemed. They are either dug 
up with a spade, or drawn from their burrows with 
a slender rod. 
Fig. g. The Piddock (Fholas dactylus) is a 
shell which is covered with sharp points and teeth 
which serve it as a rasp, by which it bores itself a 
hole in the rock. It is also a luminous animal. 
Fig. h. The Ship-worm (/eredo navalis) has 
a small thick strong shell which covers only the 
front of the body. It has a worm-like shape and 
two additional calcareous plates. It bores into even the 
hardest timber, and has sometimes caused immense 
damage to piers and harbours, as well as to ships 
Il. Molluscoidea. 
Two groups of animals intermediate between 
the Mollusca and the Worms are included in this group. 
Classul 
The Lamp-shells are bivalves like the Lamelli- 
branchiata, but there is neither ligament, foot nor 
leaf-like gills. The shells are unequal in size, and 
in many species the convex lower shell has a per- 
forated beak-like process, through which protrudes 
a stalk by which they fix themselves. 
Plate XXII. fig. k. Yerebrvatula vitrea has a 
-alcareous shell, and at the base of the flattened 
dorsal shell rises a delicate veil-like 
structure, which serves as a support for the respi- 
ratory organs, which are called arms. At present 
Class II. 
These are aquatic microscopic animals, which 
are always united to horny or calcareous supports, 
and were formerly classed with the corals. These 
frameworks are either arborescent or leaf-like, or form 
a crust over foreign substances, like the fresh-water 

calcareous 

They resemble each other in the course of their de- 
velopment, but have very little external similarity. 
Brachiopoda, 
there are few living species of 7eredratula, but they 
were very numerous at an earlier period of the 
world’s history. 
Plate XXII. fig. 1. Lewgula anatina, the Goose- 
Bill, represents the second section of the Srackzo- 
poda. ‘The tongue-shaped shells are thin and horn- 
like ; there are no arms; and the animal makes burrows 
for itself at the bottom of the sea with a long fleshy 
stalk. The genus is met with in the oldest geological! 
formations. 
Bry0zoa. 
Flumatella, in which the tentacles of the separate 
animals are arranged in the form of a horse-shoe. 
In the marine forms they are arranged in a circle. 
Eschara cervicornis (fig. m) is an illustration of the 
calcareous skeleton of a marine species. 
Subkingdom Vermes. 
(Plate XXVIII.) 
The Subkingdom of Worms is distinguished from 
that of Avtzculata by the want of jointed limbs. In the 
highest forms we indeed meet with stumps on the 
segments of the body which serve as organs of loco- 
motion, but they are never divided into separate 
joints, like those of a crab, an insect, or a spider. | 

The outer integument is always soft, and unprotected 
Only 
a few forms construct tubes to dwell In shape. 
they exhibit every transition from the long slender 
cylindrical thread-worm to the flattened tape-worm. 
by either an internal or an external skeleton. 
in. 
In the higher forms the body is divided into separate 
