MOLLUSCA. 151] 
ft consists of regularly pectinated plates. Its excretory ca- 
nal terminates at the pulmonary cavity. 
The organs of generation consist, in the female parts, of 
an ovarium, oviduct, and uterus; and in the male, of a tes- 
ticle, vas deferens, and penis, together with the peduncu- 
lated vesicle; and, as common to both the sexual organs, 
there is a cavity opening externally, in which, by separate 
orifices, the uterus, penis, and vesicle, terminate. 
As it would be impracticable to give, even in the most 
condensed form, the characters of the numerous genera which 
have been instituted, from our limited space, we shall rather 
call the attention of the reader to the structure of a few of 
the more remarkable genera. 
Genus Arton——A mucous orifice at the termination of 
the cloak. 
This genus was instituted by M. le Baron D’Audebard de 
Férussac, in his Hésteire Naturelle Générale et Particuli- 
ére des Mollusques Terrestres et Fluviatiles, folio, Paris, 
1819, 3e. liv. p. 53. The species of which it consists were 
formerly confounded with those which now constitute the 
restricted genus Limax. It differs, however, in possessing 
the mucous pore, in the pulmonary orifice being near the 
anterior margin of the shield, with the sexual orifice under- 
neath, and in the soft state of the calcareous matter, in the 
shield. ‘The author now quoted, has described four species, 
and illustrated their characters by beautiful and expressive 
figures. The Zimazx ater (together with its variety rufus) 
of British writers may be regarded as the type of the genus. 
The genus PLecrropHorts, distinguished by a conical 
protuberant shell at the termination of the cloak, was like- 
wise instituted by M. Férussac, and nearly resembles the 
preceding in form. Three species have been described 
