FAMILY 5. PLICACEA. 145 
is always of a deep violet colour both within and without. It may be 
described as being somewhat globose, turbiniform, and fragile, the spire 
being depressed, with the whorls either rounded, or acutely triangular ; 
the margins are disjoined, and the lip is very sharp, thin, and angulated 
in the middle as if with a sinus; the columella is long, straight, and 
reflected. 
Examples. 
Pl CCV... Fig.’ 1. 
JANTHINA FRAGILIS, Bory-St. Vincent. Encyclopédie Méthodique, pl.456. 
f.1.a,6. DeBlainville, Manuel de Malacologie, pl. 37. f. 1. 
Helix ianthina, Linneus. 
Tanthina communis, Lamarck. 
Pl. CCV. Fig. 2 and 3. 
TantHina ExiGua, Lamarck, Anim. sans vert., vol. vi. part 2. p. 206. 
Encyclopédie Méthodique, pl. 456. f. 2. a, b. 
Family 5. PLICACEA. 
Testa columella obliqué plicata, apertura integra, ad basem rotundata. 
Animal marinum, operculo corneo instructum. 
This family was instituted by Latreille for the reception of a small 
group of water-breathing mollusks whose shells somewhat resemble those 
of the Auriculacea, a tribe which breathe only in air. They agree with 
them in having the columella plaited, with the base of the aperture entire, 
but differ essentially in being marine and operculated, and we are some- 
what surprised that De Blainville should still refuse to separate them. 
Lamarck hastened to adopt the arrangement of Latreille even before the 
Plicacea were known to be operculated, and he has been followed in it 
by most succeeding naturalists. 
The Plicacea have a small, thin, horny operculum, and their shell is 
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