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of the lower valve, its dark frilled upper margin, and the few 

 denticles near the hinge are among its peculiarities. 



Ostrea discoidea. T. subcircularis, planulata, tenuis, pur- 

 purea : valva superior striis crebris albidis radiata ; valva infe- 

 rior major, radiatim plicoso-rugosa ; colore saturation : cavositas 

 parva, argentata, purpureo-marginata ; margine prope apicem 

 plicoso-crenulato. Long. 1^-; lat. 2 poll. Hub. ? 



The characters of the single specimen of this delicate and 

 well-formed oyster are so diverse from all others, that notwith- 

 standing the usual inconstancy of form in this genus, I think it 

 may be safely pronounced new. The small, purple-striped West 

 India Oyster (0. BrasiUana) is similar to it. 



Terebkatula caurina. T. parva, fusco-cinerea, transversa, 

 convexiuscula ; quincuncialiter punctata, costis angulatis ad 12 

 interdum bifurcatis radiata ; margine ventrali circulari, flexuoso ; 

 apice acuto, rectangulari ; lateribus rectilinearibus, incumbenti- 

 bus ; rostro bervi, vix curvato ; foramine circulari, interrupto : 

 apophysis branchialis tenuissima, angustata. Long. J- ; lat. ±^ ; 

 alt. -^ poll. Hah. Puget Sound. 



T. australis is closely allied, but is more elongated and more 

 convex ; the beak is also elongated and the ribs are less promi- 

 nent. 



Terebratula Patagonica. T. parva, solidula, albida, ovato- 

 triangularis, sub-trilobata, quincuncialiter punctata : valva oper- 

 culars plana : valva major convexa, sub-gibbosa, costis tribus 

 medianis et utrinque costis quinque divaricantibus ornata ; ros- 

 tro brevi, marginibus inflectis ; foramine magno, rotundato : 

 apophysis branchialis exilis. Long. -| ; lat. £ ; alt. ^ poll. Hob. 

 Coast of Patagonia. 



A smaller and less transverse species than the preceding, and 

 the disposition of the ribs is quite different. It is also closely 

 related to T. australis, but differs from it in the same respects. 



Terebratula pulvinata. T. tenuis, lenticularis, orbiculato- 

 trigona, albida, quincuncialiter punctata : valva minor convexa, 

 latior quam longa, marginibus lateralibus rectis : valva major 



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