56G DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [June 17, 



Distribution. Circumpolar, and throughout the North Atlantic, 

 Adriatic, Mediterranean to Smyrna, North Pacific to Mexico, Ker- 

 guelen Land, 'Challenger' Exp. (New Zealand and Falkland I.); 

 usually littoral or tidal, but occasionally living below the laminarian 

 zone. 



Fossil. Pliocene and Post-tertiary. Greenland, Iceland, Scandi- 

 navia, Great Britain and Ireland, Belgium, S. France, Italy to 

 Ustica I., Labrador and N.E. America southwards to Florida ; 

 0-13G0 ft. 



This very common species has been called by nearly twenty names. 

 It varies greatly in size, from the stunted form (incurvata) to the 

 arctic variety {gigantea), specimens of the latter being nine or ten 

 inches long. 



2. Mytilus pictus, Born. 



Mytilus pictus, Born, Test. Mus. Cses. p. Ill (1778); p. 127, 

 t.vii. f. 6, 7(1780). 



« Porcupine ' Exp., 1870 : Med. St. Capo de Gata, 51, Adventure 

 Bank. Valves only. 



Distribution. S. W. and S. France, S. Spain, Adriatic, Algiers, 

 Malta, Morocco, W. and S. Africa, Canaries; 0-10 fms. 



M. africanus of Chemnitz and M. afer of Gmelin. 



v 3. Mytiltjs adriaticus, Lamarck. 



Mytilus adriaticus, Lam. An. s. Vert. vi. p. 1 12 : B. C. ii. p. 1 16 ; 

 v. p. 171, pl.xxvii. f. 4. 



'Porcupine' Exp. 1869: St. Loch Foyle. 1870: Atl. Vigo B., 

 Tangier B. ; Med. Benzert Road, Adventure Bank. 



Distribution. Finmark to Malta and Egypt, Adriatic, Canaries ; 

 2-50 fms. 



Fossil. Pliocene and Post-tertiary. Belfast, Italy. 



Many synonyms, but all now obsolete. 



4. Mytilus incurvatus, Philippi. 



Modiola incurvata, Phil. En. Moll. Sic. i. p. 72, t. 4. f. 20. 



'Porcupine' Exp. 1870: Med. St. 50a. A single living speci- 

 men. The byssus is very long. 



Distribution. Benicarlo in Valencia ; 15 fms. 



Fossil. Pliocene. Sicily. 



My specimen, which I have considered the same species as Phi- 

 lippi's fossil, undoubtedly belongs to the species lately described and 

 figured as Modiola martorelli by Dr. Hidalgo in his excellent work 

 on the marine Mollusca of Spain, Portugal, and the Balearic Isles. 

 Through the kindness of the Abbe Biugnone, I have now had an 

 opportunity of carefully comparing his fossil specimen from Sicily 

 with my recent specimen from the ' Porcupine ' Expedition of 1870 ; 

 and I can see no difference between them, except that the former 

 has a more curved or arched contour. But this is evidently a vari- 

 able character in the recent form, judging from my inspection at 

 Palermo of a specimen sent by Dr. Hidalgo to the Marquis de Mon- 



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