EXPLANATION OF PLATES. Bg | 
Mi. — Musculus longitudinalis, a longitudinal muscle, whose use 
is uncertain. _ 
‘Br: Branchiz, gills of the right side. 
Fig. 6. Anterior aspect of the cartilaginous base of the skull, of its 
natural size. This aspect supports the brain. 
Fig. 7. Posterior aspect of the same cartilage. 
S. Aspectus superior, superior aspect. 
5 Aspectus inferior, inferior aspect. 
De. Aspectus dexter, right aspect. 
Sn. Aspectus sinister, left aspect. 
Ap.@. (é£sophagi apertura, the aperture for the passage of the 
cesophagus into the stomach. 
PLATE Tl. 
The intention of this Plate is to demonstrate the nomenclature of 
the external parts of the testaceous animals of the Class Gastero- 
poda. 
Fig. 1. Helix aspersa, creeping against a window, and thus showing 
its four tentacles, the two eyes, the mouth, the under lp, the 
neck, the lower border of the mantle, the lateral aperture, and 
the undulations of the muscles of the foot when creeping, in 
their natural position. 
Fig. 2. Helix aspersa, an open-turreted variety creeping and show- 
ing its back. 
Fig. 3. Trachea nemoralis, a slightly-turreted variety. 
Fig. 4. Gulnaria peregra, creeping. — 
Fig. 5. Gulnaria peregra, swimming, when the under part of its 
foot glides along the surface of the water, the shell being im- 
mersed. 
Fig. 6. Ancyclus fluviatilis, creeping. 
Fig. 7. Planorbis marginatus, creeping. 
Fig. 8. Planorbis marginatus, swimming, showing the umbilicus of 
the shell. 
Fig. 9. Bithynia impura, creepmg, showing the position of its oper- 
culum. 
Fig. 10. Buccmum undulatum, creeping and showing its syphon or 
respiratory tube, and the channel or groove in the shell through 
which it passes, when the animal is withdrawn into the shell. 
Fig. 11. Patella vulgata, the under view, showing its external bran- 
chi, gills, the foot, borders of the mantle, and the tentacula. 
