13. C. discors, Linn. {Mytilus.) — Modiola d. and discrepans. — Brit. co. 



generally, among seaweeds, C. Wedge-shaped and lobed. 



14. C. marmorata, Forbes. — Mytilus and Mediola discors, discrepans, 



and tumida. — Brit. co. generally, Cc. Rhomboidal, marbled. 



15. C. costulata, Risso. — Exmouth, Cornwall, Swansea, Herm. 



Wedge-shaped, marbled, strongly-ribbed. 



16. C. rhombea, Berkley, {Modiola.) — M. Prideauxiana. — Guernsey, 



Torbay, Penzance, etc. ; coralline, R. 



17. C. decussata, Montagu, {Mytilus.) — C. and Modiola elliptica, 



cicercula, 'dw^faba. — Scarborough, and a few northern localities, 

 5 to 50 fath., Mc. ; Norway, etc. Subquadrate, decussated, 

 minute. 



Mytilus, Linn. 



18. M. edulis, Linn. — M. vulgaris. — Brit. co. generally, Cc. Byssal 



margin swelled. 



19. M. ungulatus, Linn. Syst. Nat. — M. edulis, var. M. incurvatus 



(Hoof-Mussel). — Cornwall, Guernsey, etc., Mr. Byssal margin 

 bent inwards, lower margin broad and straight. 



20. 21. M. galloprovincialis, Lamk. — M. edulis, var. M. dilatatus?, 



M. pellucidus ? (young, f. 21), M. subsaxatilis ? — British Chan- 

 nel, etc., C. Dorsal margin dilated, beak advancing. 





