MAZATLAN BIVALVES 



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

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

 witJi Cbama Pspinosa attaclied, and 3 fine specimens of D. 

 Cumingu m situ. One is removed from its nestling place be- 

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



CLASS . LAI^IELLIBRANCHIATA, Blamv'. 

 Concbifera: Lam PMl. Zool. 1809; An s. Vert. v. 411, ed. 2, 



rsi;^ 18?' ^"' ^^' ^*^' P- ^2 ' ^'''- ^''^- ^''^ 



Acephak LameUibrancMata : Jiang, Man. Moll. 272.-Forhes 



and Hani. Br. Mol. i. oo.-Clarl; Moll. Test. Mar. Br. 23. 



Pamilt PHOLADID^. 

 Pboladidge, Gray, P. Z. S. 



Genus PHOLADIDEA, Turf. 

 Pbolas, Lin. Lam. 



15. PhoLADIDEA MELAJftJEA, SoW. 



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

 Conch. 1849, p. 499.-i?. J/. Cat. D-Qrh. Shells, no 479, p. 56.' 

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

 sparhatula, and concamerata, which last represents it on the 

 Oabfornian coast. In its posterior cup-liie appendages, it re- 

 sembles Talona clausa from the Gambia. The sheU is extremely 

 thin, shewing inside a row of oblong tubercles impressed from 

 without on the Ime separating the anterior and posterior por- 

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

 strong, and waving • and passmg over the medial depression 

 at an angle slightly mdeniug as the sheU becomes adiUt are 

 contmued, ccmcentric and straight, 'graduallv fading as 'they 

 approach the posterior extremity. This is covered with a thick 

 epidermis, endmg m a short double cup, which is bi-lobed 

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

 carried in a Hat ex-pansion round to the umbos. The lar-^est 

 specimen measures, with the cup, long. "9, lat. I'So, alt. S'l 

 Sah.—ln hard clay and loose stones at low water, Monte Christi 



(Oniayaqiul), CwT/^i^^-.-Ecuador, Afonte Christi, D'Orbigny. 

 Mazatlan; m company with P. acuminata, extremely 



rare ; Lpool Col. ^ 



Tablet 21 contains the most characteristic (though a some- 

 what imperfect) specimen. 



