08. P. Dactylus, Linn.—P. hians, P. callosa.—Eng., Scot., Ire., C. Dorsal plates four; hinge pitted.
09. P. candida, Linn.—Eng., Scot., Ire., C. One dorsal plate; valves not beaked.
10. P. parva, Penn.—P. callosa, P. tuberculata.—Salcombe, Belfast, Cornwall, etc., M. C. One dorsal plate; valves beaked.
11. P. crispata, Linn.—P. bifrons.—Hastings, Liverp., Scarb., Dubl., Forth, etc., C. No dorsal plate; valves broad, beaked, with oblique division.
13. P. striata. Rare and doubtful as British. Valves closed.
Pholadidea. Pierces and inhabits stone.
12. P. papyracea, P. Loscombiana, P. Goodalli.—S. Devon, N. Ire., R. Valves closed, with a cup. P. lamellata, Turt., when young, not closed; no cup.
Gastrochæna. Bores and inhabits stone, thick shells, etc.
14. G. modiolina, Lamk.—G. Pholadia, G. hians, Mya dubia, Mytilus ambiguus, Pholas faba.—Torbay, Birterbuy, Galway, Weymouth, etc. Valves thin, gaping, enclosed in bottle-shaped tube.
Saxicava. Bores and inhabits stone.