20 CLASS III. GASTEROPODA. ORDER III. CERVICOBRANCHIATA. 
They are, however, very differently disposed of by Gray ; the Siphonariz 
are regarded by this author as being pulmoniferous ; he asserts, that 
although inhabiting the sea, they are compelled to rise to the surface of 
the water in order to breathe air, like the freshwater Ancyli; and they 
are consequently placed by him in his order Pneumonobranchiata, in com- 
pany with the Lymnee, Helices, Cyclostomata, and the rest of the air- 
breathing Gasteropoda ; the truth of this hypothesis however remains to 
be determined. 
The shell of Siphonaria may be described as being orbicular, dish- 
shaped, or of the form of a depressed cone, and generally crenated at the 
basal margin ; the vertex is somewhat oblique, and recurved backwards. 
The muscular impression is interrupted anteriorly, and the right side of 
it is characterized by the appearance of a canal or siphon. 
Examples. 
Pl. CXXXVIIT. Fig. 1. 
SrpHONARIA ATRA, Quoy and Gaimard, Voy. de l’Astrolabe, vol. ii. p. 337. 
pl. 25. f.41 and42. Deshayes, new edit. of Lamarck, vol. vii. p. 560. 
Siphonaria picta? D’Orbigny. 
Pl. CXXXVIUI. Fig. 2. 
SIPHONARIA DENTICULATA, Quoy and Gaimard, Voy. del’ Astrolabe, vol. ii. 
p. 340. pl. 25. f.19and 20. Deshayes, new edit. of Lamarck, vol. vii. 
p. 099. 
Pl. CXXXVIII. Fig. 3. 
SrpHonaria cHAractErRistica, Nobis, Proceedings Zool. Soc., 1842. 
Pl. CXXXVIII. Fig. 4 and 5. 
SIPHONARIA OBLIQUATA, Sowerby, Appendix to Tankerville Catalogue. 
Pl. CXXXVIIL. Fig. 6. 
SIPHONARIA G1GAs, Sowerby, Appendix to Tankerville Catalogue. 
