490 



postice truncata; costis moniliferis radiatis et lineis concentricis 

 cancellata; umbonibus subcentralibus^ margine dorsali reflexo. 



A wide, rather flat shell, widely gaping in front, and truncated 

 at the posterior extremity, with radiating ribs forming knots on 

 the raised lines of growth. It appears to be without accessory 

 valves. 



Taken in Manilla Bay. Cuming. 



17. Pholas Darwinii (pi. cvii. f. 76, 77), Soioerbi/, junr., 

 Pro. Zool. Soc, 1849. 



Ph. testa brevi, late aperta, in medio area constricta divisa ; 

 antice radiatim scabra ; ad marginem veutralem Isevi, recedente, ad 

 marginem dorsalem arcuatira reflexa ; postice concentrice striata, 

 ad extremitatem posticam margine valide recurvo. 



A very remarkable shell, rather sliort, widely opening in front, 

 divided in the centre by a constricted grove. Before the grove it 

 is roughened by undulated lines of growth, forming radiating 

 ribs. The ventral margin is smooth, and recedes towards the 

 dorsal part, where it is turned over so as to form a broad reflected 

 edge reaching to the umbones. Posterior to the dividing line it 

 is marked by raised lines of growth, and gapes widely ; at the end 

 there is a broad extension of the shell curved outwards. 



Collected by Mr. Darwin at Chiloe. 



18. Pholas Teeedin^formis (pi. cviii. f. 97, 98), Sowerhy, 

 junr., Pro. Zool. Soc, 1849. 



Ph. testa globosa, aperta, in medio divisa ; antice margine ven- 

 trali subangulata ; costis laqueatis concentricis ornata ; postice 

 brevi, laevigata ; lamina dorsali una subquadi'ata, super marginem 

 reflexam testee posita. 



A small, globose species, in some degree resembhng the young 

 of P7i. clavata, &c., but differently sculptured; and although it has 

 the appearance of a mature shell, it is quite possible that it may 

 belong to that group, and its being in so soft a substance as wax 

 may be the reason for the enclosing laminge not being formed. 

 This and the next species {Ph. aperta) were at fii'st thought to 

 belong to the genus Xylophaga ; but, on examination, were found 

 to possess the cm-ved processes in the hinge, which are charac- 

 teristic of the genus Pholas, and are not found in Xylophaga. 



Pound in cakes of floating wax on the coast of Cuba. 



