192 
bably deposited in an extensive lake. This opinion is 
strengthened by the discovery of Cypris (see t. 485.) in 
some of the beds connected with the formation, while the 
presence of oysters excites much speculation. It has been 
justly observed, that the shells referred to Paludina (Vivi- 
para, Min. Conch. t. 31.) are thicker than the recent 
species of that genus, and approach very near to Turbo 
littoreus; but the general form is nearer to Paludina flu- 
viorum, and we have never been able to extract an indi- 
vidual with a perfect lip. The Cyclades have been better 
determined, the hinge having been freed from the stone 
(see t. 527.). The shells immediately under our consi- 
deration, although very abundant, are never very perfect : 
casts of their interior are most frequent ; and they present 
strong indications of the deep muscular impressions, the 
laminated lateral tooth, and the large teeth in the hinge, 
characteristic of the genus Unio; so that we cannot choose 
but arrange them under that genus of freshwater shells ; 
and although it must appear extraordinary to find oysters 
mixed with freshwater shells, or a freshwater formation 
between marine deposits, we must not, however praise- 
worthy it is to admire, lose ourselves in wonder, but 
steadily persevere in searching after the whole truth; for 
by so doing we shall best display the harmony that exists 
in all the works of Nature, and prove that we possess 
a mind open to conviction, the possession of which is an 
enjoyment we must ever feel grateful for to Him who 
gave it. 
