1. Genus Pholas. Pl. [VI].
Animal. Without a tubular sheath, projecting anteriorly into two united tubes, frequently surrounded by a common skin, and the posterior extremity provided with a short muscular foot, flattened at its extremity.
Shell. Multivalve, equivalve, transverse, gaping at both ends, with various accessory pieces either on the hinge or below it. Inhabits the Indian seas and American shores. Eighteen species.
- Pholas dactyla.
- P. orientalis.
- P. candida.
- P. dactiloides.
- P. papyracea.
- P. tuberculata.
- P. silicula.
- P. callosa.
- · · · · ·
- P. costata.*
- P. clavata.*
- P. ovum.*
- P. lancellata.*
- P. crispata.*
- P. truncata.*
- P. californica.*
- P. penita.*
- P. oblongata.*
- P. cuneiformis.*
2. Genus Gastrochæna. Pl. [VI].
Animal. Unknown.
Always without accessory pieces, therefore easily distinguished from the Pholas.
Shell. Equivalve, somewhat cuneiform with a very large oval and oblique aperture anteriorly; posterior extremity nearly closed; hinge linear; marginal and without teeth. Three species.
- Gastrochæna cuneiformis.
- G. mytiloides.
- G. modiolina.