Some Manitoba Cladocera, with Description of One New Species

The hard parts, exoskeletons, of crustacea contain varying intermixtures of calcite and phosphate of lime. The bryozoans have cases composed of a mixture of calcite and aragonite. The brachiopoda have shells composed of calcite and some phosphate of lime, the latter salt being almost limited to the shells of the inarticulate division of this class-linigulca crania discina, etc. In the lamellibranchs there is found some variation in the composition of shells of different genera, in some the shells are wholly aragonite, in oysters and scollops (Ostrea, Pecten) the shells are calcite, whereas in mussels Mytiltus and Pinnas, the outer layer is calcite, the inner aragonite.