"The family Pholadaria contains,
| Pholas. | Pholas, stone-piercer. |
| Gastrochæna | Pholas and Mya. |
"Notwithstanding the accessory pieces of the hinge, Pholas is placed among bivalve shells, the essential character of which is to have two valves united by a hinge. The Pholas has a foot or strong muscle, very thick and short. In the next genus, composed of Pholas hians and Mya dubia there are no secondary valves.
"Allied to this family is Xylophaga dorsalis, a curious shell. One specimen has been lately found at Gravesend, upon a stick.
[A] See Penny Cyclopædia, article Clavagella.
"Solenacea includes
| Solen | Solen. |
| Panopæa | Mya. |
| Glycimeris | Mya. |
SOLENACEA.
MYARIA.
MACTRACEA.
"The Solen is furnished with a muscle, called by some writers a tongue. By the aid of this instrument they descend two feet deep in the sand. The tongue is first projected from the shell, and cuts a hole. It then assumes the form of a hook, and draws down the shell into the hole. This operation is repeated until the shell disappears. Panopæa is a large shell—it is in the Museum.