PELECYPODS are a class of MOLLUSKS having shells composed of two valves, usually of equal size. A line of symmetry can be drawn between the two valves. Clams, oysters, mussels and scallops are living types. The group is represented in Paleozoic times by an increasing number of simple forms in which the gill apparatus and the hinge between the two identical valves are of primitive structure. More complicated types appear in the Mesozoic and Cenozoic eras.

The SCALLOP, imbedded in the rock fragment shown in the first picture, is representative of a large number of Ordovician Pelecypods of Southern Ontario. The novice at fossil hunting can discover and identify "millions" of Pelecypods along river beds. The CLAM in the cecond photograph was carefully loosened from its limestone matrix by a hammer and small cold chisel. Clams, like the snails which follow, are usually poorly preserved and difficult to identify. They are also less numerous than the scallops; both were collected on a walk along the river bed from Magwood Park to Baby Point.

GASTROPODS are the largest class of MOLLUSKS. They have a single valved shell which contains a broad foot and a well-developed head with eyes, mouth and tentacles. Most snails have spiral shells. Other Gastropods are slugs (without shells), conchs (marine snails typically with coiled shells), whelks and limpets.

These loose SNAILS were collected from an abundant supply in the silty matrix beneath the Bloor Street West bridge.

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