78 CLASS III. GASTEROPODA. ORDER VI. PULMOBRANCHIATA. 
The shell of Clausilia may be described as being turrited, elongated, 
fusiform, and always turned to the left; the spire is rather obtuse, and 
composed of many whorls, gradually enlarging as they are formed, the 
last being characterized by having a slight groove in front of the mouth 
forming a ridge or keel ; the aperture, which is irregular and rotundately 
ovate, is furnished with a greater or less number of tooth-like plaits, as 
also with a small, elastic, shelly bone, attached to the columella ; this little 
accessory organ is destined to close the aperture after the animal has 
withdrawn itself into the shell, and it again yields with the slightest 
pressure of the animal when it wishes to crawl forth ; the margin of the 
aperture is continuous all round, and the lip is reflected back. 
In one of our figures of the Clausilia Macascarensis the shell is repre- 
sented with a portion of the last whorl removed, to show the clausium. 
Examples. 
PI. CLXXI. Fig. 1. 
Crausitia Macascarensis, Sowerby, Genera of Shells, No. 30. 
Pl. CLXXI. Fig. 2. 
CLAUSILIA TORTICOLLIS, Lamarck, Anim. sans vert., vol. vii. p. 197. 
Helix (Cochlodina) torticollis, De Férussac. 
Bulimus torticollis, Olivier. 
Pl. CLXXI. Fig. 3. 
CiausiLia LaBiata, Olivier. Sowerby, Genera of Shells, No. 30. 
Turbo labiatus, Montague. 
BULIMUS, Bruguiere. 
Testa ovata vel oblonga, interdum subturriculata, anfractibus plus mi- 
nusve numerosis, ultimo majore; apertura integra, intus nonnun- 
