02 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



M. decussatus, Lain. (= M. Americanus, Orb., M. Orbignyanus, Hupe, 

 M. crenatus (Lam.), Morch), considered by some authors to comprise 

 two species, but on tbis point I am unable to speak. 



6. Mytilus exustus, Linn. 



Mytilus exustus, Linnams : Syst. nat., 10th ed. (1758), p. 705 ; 12th ed. 



(1766), p. 1156. 

 ,, „ Linn. : Lamarck, Anim. sans Vert., vol. vi (1819), 



p. 121. 

 „ ,, Lam. : Reeve, Conch. Icon., vol. x (1858), fig. 10. 



„ ,, Lam. : Clessin, Conch. -Cab., 2nd ed. (1887), p. 42, 



pi. xvi, figs. 7, 8. 

 ,, Domingensis, Lam.: Clessin, loc. cit . , p. 79, pi. xi, figs. 15, 16. 

 ,, exustus (Lam.), Reeve : (Smith, Journ. Linn. Soc, vol. xx 



(1890), p. 499. 

 ,, atropurpureus, Dunker: Clessin, loc. cit., p. 32, pi. xi, figs. 1, 2. 

 ,, exustus, Lam. : Dall, Trans. Wagner Inst., vol. iv, p. 788 ; 



Nautilus, vol. x (1897), p. 123. 

 ,, Domingensis, Lam. : Jhering, Rev. Mus. Paulista, vol. ii 



(1897), p. 96. 

 ,, cubitus, Say: Clessin, loc. cit., p. 43, pi xvii, figs. 5, 6. 

 ,, Adamsianus, Dunker: Reeve, loc. cit., sp. 55. 



This is a solid shell, with terminal umbones, strongly bifurcate, 

 ribbed, with yellow periostracum, sometimes marked with purplish- 

 brown zones and spots. D'Orbigny has not recorded this species, 

 which does not occur in Southern Brazil, his M. Domingensis belonging 

 to the following species. The present species occurs from the West 

 Indies to Pernambuco (Smith) and Bahia (Jhering). It seems that it 

 exists also on the West African coast, but I have not the necessary 

 material for studying the question with relation to the allied African 

 and Indian species. The Panama representative is M. Adamsianus, 

 Dkr., which does not appear to be a distinct species. 



Subgen. HORMOMYA. 

 7. Mytilus Domingensis, Lam. 



Mytilus Domingensis, Lamarck: Anim. sans Vert., vol. vi (1819), 



p. 122. 



,, ,, Lam. : Orbignv, in Sagra's Hist. nat. Cuba, 



Moll., vol. ii [ 1846?], p. 328; Voy. Amer. 



merid., torn, v [1846], p. 645. 



,, ,, Lam. : Hidalgo, Mol. Viaj. Pacifico, pt. ii (1869), 



p. 54, pi. ii, fig. 6. 

 ,, Orbignyanus, Clessin: Conch. -Cab., 2nd ed., p. 87 (1887), 

 pi. xxv, figs. 1, 2. 

 Modiola sulcata, Lam. : Clessin, loc. cit., p. 123, pi. xxxi, figs. 9, 10. 

 Mytilus atropurpureus (Dunker MS.), Reeve : Conch. Icon., vol. x 

 (1858), fig. 11. 



