* Dentàlium, tooth-shell, ex. D. elephantìnum.
* Sérpula, worm-shell, ex. S. triquétra.
Terèdo, ship-worm, ex. T. navàlis.
* Sabella, Sabella, ex. S. Belgica.
Total number of genera in the arrangement of Linnæus, thirty-six.
The genera marked with an asterisk, contain species found in Britain.
CHITON.
LEPAS.
"Multivalves may be divided into two kinds, the pedunculated, or those fixed to other bodies, as rocks, stones, planks, &c.; or free, as the Chiton and Pholas.
"Our first genus is Chiton. The shell is easily known. The fixed character is, many valves placed over each other along the back. I have already noticed the membrane which connects the valves, which is also a permanent character. It is elastic: the sides are either scaly, as in C. squamòsus, ([Plate 1],) and hairy, or spinous. The species are determined by the margins. Some of the Chiton genus are common upon our own coasts; they are frequently found among seaweed and stones, rolled up like a ball. C. fasciculàris and C. lævis are British; there are some other British species. The animal adheres to rocks, like the Patella, or limpet. The number of species forty.