15. S. rugosa, Linn.—Mytilus r., Hiatella r., S. gallicana, S. pholadis, Byssomya pholadis, Mya byssifera.—Eng., Scot., Ire., C. Valves oval.
16. S. arctica, Linn.—(Mya) Hiatella a., Anatina a., Hiatella minuta, Solen minutus, S. rhomboides, Agina purpurea, Solen p.—Eng., Scot., Ire., C. Valves rhomboidal; angle serrated.
Omitted.—S. fragilis, Nyst. Not the young of S. rugosa. Vigo Bay.
Petricola. Inhabits stone.
17. P. lithophaga, Retz.—P. striata, costellata, rocellaria, ruperella, Lamk., Mya and Sphænia decussata.—Cork, Bristol, R. as British.
Venerupis. Bores and inhabits stone.
18. V. Irus, Linn. (Donax).—Tellina cornubiensis, Cuneus foliaceus, Petric., and Pullastra, I.—In limestone at Plymouth and other southern coasts. Wedge-shaped.
Mya. Burrows in mud and sand.
19. M. truncata, Linn.—M. ovalis and Sphænia Swainsoni (young).—Various localities and depths, C. Truncated at end.
20. M. arenaria, Linn.—Herne Bay, Portsmouth, etc., C. Tapering at end.