4 MANUAL OF THE MOLLUSCA. 
divided them into three classes, founded on the modifications of 
their feet, or principal locomotive organs. 
1. The cuttle-fishes constitute the first class, and are termed 
Aten 
sonty 
4a ieee 
Lon} 
6) ©-O.0: 
COGS 
BOHRA RTE 
Fig. 1.* Oral aspect of a Cephalopod. 
Cephalopoda,t because their feet, or more properly arms, are 
50 attached to the head as to form a circle round the mouth. 
2. In the Gasteropoda,} or snails, the under side of the body 
Fig, 2. A Gasteropod.§ Fig. 3. A Pteropod. | 
forms a single muscular foot, on which the animals creep or 
glide. 
homologous in the vertebrata and in the mollusca. When applied to the latter, the 
terms are vague and indefinite in meaning. 
* Fig. 1. Loligo vulgaris, Lam.%. From a specimen taken off Tenby, by J. S. 
Bowerbank, Esq. The mandibles are seen in the centre, surrounded by the circular 
lip, the buccal membrane (with two rows of small cups on its lobes), the eight sessile 
arms, and the long pedunculated tentacles (¢), with their enlarged extremities or clubs 
(e). The dorsal arms are lettered d, the funnel f. 
¢ From cephale, the head, and poda, feet. See the frontispiece and pl. I. 
$4 Gaster, the under side of the body. 
§ Fig. 2. Heliz desertorum, Forskal. From a living specimen in the British Museura, 
March, 1850. 
{ Fig. 3. Hyalea tridentata, Lam., from Quoy and Gaimard, 
