MOLLUSCA. 
487 
melkij but a prominent plate on the apertural wall. * Cox, Monogr. Austral. 
Land-shells, p.81, pi. 12. fig. 16. 
Clausilia, Tlie natural arrangement of the European species 
is the object of two valuable publications — one by W, v. Vest, 
in the Transactions of the Transylvanian Society of Natural 
Sciences, and the other a separate publication by Ad. Schmidt. 
V est describes with great accuracy the situation and function of 
the several plaits within the aperture of the shell. The upper- 
most or first palatal plait acts as a hinge on which the outer edge 
of the clausilium moves ; the lunella or lunar plait is a modified 
undermost or fourth palatal plait, and where it occurs the clau- 
siliuin is not notched. The larger the clausilium, tlie smaller are 
all the plaits ; the extreme development of this occurs in Cl. con- 
cilians (Ad. Schmidt), the least in the section Alopia, especially 
in the species elegans (Bielz) and canescens (Parr.). An ac- 
cessory palatal plait, above the first, exists in the sections 
Medora and Delima. The columellar plait offers to the clau- 
silium a point against which leans either the base only or the 
whole inner margin ; but in some sections of the genus the clau- 
silium never comes into contact with this plait. The spiral lamella 
serves for guiding the movement of the clausilium ; the columellar 
plait and the inferior lamella form together a recess, in which 
the clausilium is secured whilst the animal is moving about. 
The broader and the more curved the inferior lamella, the larger 
is also the clausilium and the more developed its outside lobe. 
Vest establishes three principal divisions: — 
I. Claugiliiim bilobed, no lunella ; palatal plaits 3-4 ; clausilium far from 
the columellar plait. Sections Alopia, Marpessa, and Triloba. 
II. Clausilium S-sliaped, its tip somewhat rounded or concavely bent out- ' 
wards ; palatal plaits 1-3 ; clausilium rarely reaching to the columellar 
plait. Sections Siciliaria, Medora, Alhinaria, Agathylla, Cristataria, HerUla. 
III. Clausilium entire ; rarely more than two palatal plaits ; lunella gene- 
rally present ; clausilium generally touching the columellar plait. Sections 
Delima, Isahellaria, Papillifera, Dilataria, Phcedusa, Uncinaria, Fusulus, 
Olympa, Gracilaria, Pyrostoma, Trigonostoma, Mentissa, Iphigenia, Idyla, 
Strigillaria, Alinda, Nenia. 
Ad. Schmidt, to whom the preceding paper was known, re- 
fuses to use these subgeneric names, thinking they designate di- 
visions of very unequal value, and contents himself with establish- 
ing six principal divisions, without distinguishing them by names. 
He calls them arecc \ and there are within each several circles 
of forms,^^ named from the principal species : — 
His first division comprises the circles of Cl. orthostoma (Mouss.), hielzi 
(Parr.), the so-called Bako-clausilice, further the circles of Cl. plnmhca 
(Rossm.), parreyssi (Ziegl.), laminata (Mont.), and some other species ; there- 
fore this division corresponds to the two subgenera Alopia and Marpcssa of 
other authors. Among the Palco-clausilm he includes also (A«7cn) glauca 
