Mr. L. Reeve on the recent Orbiculse. 131 



geographical distribution that the fauna of the West- African sea 

 north of Sierra Leone, whence O. ostreoides is supposed to have 

 come, is in part identical with the fauna of the seas of California 

 and the West Indies. Our British Phasianella pullttj which 

 ranges southward to West Africa, appears also in the West 

 Indies; and when preparing my monograph of Terebra in 

 ' Conch. Iconica,' I had no hesitation in declaring that T, varie- 

 gatttf Africana, Hwpei, intertinctaj marginata, albocincta, Hindsii, 

 and subnodosa, described by various authors from the mouth of 

 the Gambia, Senegal, Mazatlan, and California, are all varieties, 

 and but slightly varying varieties, of one and the same species. 



2. OrUcula stella, Gould, Exped., Shells, Proc. Bost. Soc. 1846 ; 

 Otia Conch, p. 120. 



Discina stelld, Gould. 



Hab. China Seas ; Wilkes. Singapore and Philippine Islands ; 

 Cuming. 



This species has a wide distribution in the Eastern seas. On 

 comparing authentic specimens received from Dr. Gould, col- 

 lected in the China Seas by Wilke^s Exploring Expedition, I find 

 them identical with specimens, attached to fragments of Pul- 

 lastrttj Pinna, and Malleus, collected by Mr. Cuming at Singa- 

 pore and at the Philippine Islands. The sculpture varies in 

 strength. In young specimens, as stated by Dr. Gould, the 

 radiating striae are scarcely developed; in older specimens, that 

 have had to contend with irregularities in their place of attach- 

 ment, the sculpture has a minutely latticed character, like the 

 grain of a thimble. The under valve is thinly membranaceous, 

 or thicker, concave or convex, according to circumstances of 

 habitation ; and the position of the slit obviously varies with the 

 position of the vertex in the opposite valve. On a flat place of 

 attachment the shell is symmetrically orbicular, and the vertex 

 and subcumbent slit are nearly central ; but when attached to 

 a sloping or declivitous substance, the vertex is pressed to one 

 side, and the slit of the under valve follows the same direction. 



3. Orbicula Antillarum, D'Orbigny, Moll. Hist. Cuba, 1853, 

 p. 368, pi. 28. figs. 34-36. 



Hab, Cuba, Martinique. 



Mr. Cuming possesses specimens of 0. Antillarum, both from 

 Cuba and Martinique, in all of which the vertex is inclined 

 posteriorly, while the shell is less cancellated than in the Eastern 

 O. Stella ; but the shells are wonderfully alike in their general 

 aspect. 



10* 



