34 
PROCEEDINGS OF THE SCIENTIFIC ASSOCIATION. 
a thin horny suboval operculum -with a submarginal nu- 
cleus. 
Marita cornu-arietis Linne. 
Helix cornu-arietis, Linn. 
Planorbis cornu-arietis, Lam. 
Ampullaria cornu-arietis, Sowerbg, Genera. Amp. f. 3. 
,, - ,, JPood, Lnd. Test. Helix 55. 
Marisa Knorrii Phillippi. 
Ceratodes fasciatus Guilding. 
This discoid planorbiform type of Ampullaria will rea- 
dily be recognised. It occurs in most of our streams, 
and visitors to the Botanic Garden may observe numbers 
of the molluscs of this species in the basins of the foun- 
tains. It prefers still waters and ponds, to which the 
form of its shell is adapted. 
It is found in various parts of South America and in 
St. Vincent. 
Diameter 35 mill, height 12 mill. 
The var. Swifti is smaller and the spire is somewhat 
above the last whorl. 
Paludestrina D’Orbiguy 1841. 
Fluviatile Operculata with turreted or subglobose opaque 
shells without umbilicus or canal, having a thin horny 
paucispiral operculum with a sub-central nucleus. 
Paludestrina spiralis Guppy. 
Bithinia spiralis Guppy , Ann. Mag. Nat. Hist. 3 ser. 
vol. xiv, p. 244. 
Paludestrina spiralis, ib y Ann. Sf Mag. N. H. 3 ser. vol. 
xvii, p. 43. 
A small dark-brown or reddish-brown opaque turreted 
shell with spiral lines and sometimes a row of low spines 
