86 Lamarck’s Genera of Shells. 
divides the conchifera tenuipeda into the four families con- 
tained in this section. | 
lst Family. 
Mactracea. 
Foot of the animal small, compressed, and calculated for 
locomotion. 
Shell equivalve, generally gaping at the lateral extrentities. 
Ligament internal, with or without any external ligament, 
1. Lutraria*. 
Shell inequilateral, transverse oblong, or rounded, gaping at 
the lateral extremities. Hinge with one tooth, folded, as it 
were into two, or two teeth, one simple, with an adjacent, 
oblique, deltoid pit, projecting inwards. No lateral teeth. 
Ligament internal, fixed in the pits. 
The lutrariz are distinguished from the mactre by having no 
lateral teeth. The hinge presents on each valve a compressed 
protuberance, hollowed above, into a pit, and on one side, one 
or two teeth, one of them folded, as it were, in two, the other 
simple. 
Type. Lutraria solenoidest. Mya oblonga. Gmelin. 
Shell oblong, with transverse rugose striz; anterior side 
very long, apex rounded, very gaping. 
European Ocean. PI. iv. Fig. 31. 12 Species. 
[To be continued.] 
Art. VIL. Experiments on the Oxides and Salts of Uranium. 
Ir is generally stated, upon the authority of Bucholz and 
Schoubert, that there are two oxides of uranium, but the fol- 
lowing experiments appear to render this opinion very doubtful. 
A quantity of oxide of uranium was prepared, as usual, from 
the native oxide (pechblende), and converted into nitrate, by 
solution in nitric acid and crystallization. The crystals were 
dissolved in water, and were found still slightly contaminated 
* Lutra, an otter, from /utum, mud, because it frequents muddy places. 
+ Solen-like. 
