44 GASTEROPODA. SACCOBRANCHIA. 
ORDER III. SACCOBRANCHIA. 
Pulmones, Cuvier. 
Branchie saccum interné tegentes, non elevate. Testa 
nulla; interna; aut externa, spiralis vel capuliformis aut sub- 
conica. Operculum externum nullum. Sewus hemaphroditus. 
Familiarum Synopsis. 
* Tentacula 4: superiora ad apicem oculigera. 
Fam. 1. Limacip#. Corpus sepius nudum, elongatum, 
supra anticé disco thoracico instructum. Testa seepius interna, 
nunquam elevato-spiralis. 
Fam. 2. Henicip#. Corpus spirale. Testd spirali tectum. 
** Tentacula duo. 
Fam. 3. Carycurapz. Corpusspirale. Testd spirali tec- 
tum. Apertura dentata. 
Fam. 4. Limnap#. Corpus seepius spirale. Testa seepius 
spiralis, seepé depressa. Aperturd mermi. 
Fam. 5. ANCyLIp&. Corpus ovato-aut elongato-conicum. 
Testdé conformi tectum. Spira inchoata. 
The respiration of all the animals of this Order is performed 
by the lining of a sac, the entrance to which is a contractile 
trachea, formed from the mantle, and is opened or closed at 
the will of the animal, who ejects the air by the trachea when 
it has performed the purposes of respiration, and takes in a 
fresh supply through the same opening, which it then closes. 
The body is either naked, or covered by a shell. In the 
first family, the Limacide, the shell is mternal, and situated 
beneath a thoracic dise ; is wanting entirely, or is replaced by 
a few obsolete shelly fragments. In the families Helicide, 
Carychiadee and Limnadez, the bodies are spiral, and are pro- 
adel 
