MAZATLAN BIVALVES 



Tablet 18 contains 8 valves, very young, in test tube. Tablet 

 19 contains 4 adult valves. Tablet 20 contains Ostrea Virginica, 

 with Chama Pspinosa attached, and 3 fine specimens of D. 

 Cumingii in situ. One is removed from its nestling place be- 

 tween the Chama and Oyster, and laid open to shew the inside. 



CLASS LAMELLIBRANCHIATA, Blainv. 



Conchifera : Lam. Phil. Zool. 1809 ; An s. Vert. v. 411, ed. 2, 

 vi. 1. aray, Syn. B. M. 1840, 1842, p. 72 ; Proc. Zool. Soc. 

 1848, p. 183. 



Acephala Lamellibranchiata : Rang, Man. Moll. 272. Forbes 

 and Hani. Br. Mol i. 55. Clark, Moll. Test. Mar. Br. 23. 



FAMILY PHOLADZD^E. 

 Pholadidse, Gray, P. Z. S. 



GENUS PHOLADIDEA, Turt. 

 Pholas, Lin. Lam. 



15. PHOLADIDEA MELANUEA, Sow. 

 Pholas melanura, Proc. Zool. Soc. 1834, p. 70. Sow. Thes. 



Conch. 1849, p. 499. .R M. Cat. D'Orl. Shells, no. 479, p. 56. 



This belongs to the same group of species as tridens, quadra, 

 spathatula, and concamerata, which last represents it on the 

 Californian coast. In its posterior cup-like appendages, it re- 

 sembles Talona clausa from the Gambia. The shell is extremely 

 thin, shewing inside a row of oblong tubercles impressed from 

 without on the line separating the anterior and posterior por- 

 tions, as well as the anterior ridges. These are closely set, 

 strong, and waving ; and passing over the medial depression 

 at an angle slightly widening as the shell becomes adult, are 

 continued, concentric and straight, 'gradually fading as they 

 approach the posterior extremity. This is covered with a thick 

 epidermis, ending in a short double cup, which is bi-lobed 

 outside and simple within. The adult closing of the valves is 

 carried in a flat expansion round to the umbos. The largest 

 specimen measures, with the cup, long. '9, lat. 1*85, alt. 8 '6. 

 Hob. In hard clay and loose stones at low water, Monte Christi 



(Guayaquil), Owming. Ecuador, Monte Christi, D'OMgny. 



Mazatlan ; in company with P. acuminata, extremely 



rare ; Lpool Col. 



Tablet 21 contains the most characteristic (though a some- 

 what imperfect) specimen. 



