39G balanim:. 



3. Chelonobia patula. PI. 14, fig. 3 a, 3 b, 4. 



Coronula patula. Rcinzani. Memoire di Storia Naturale (1820), 



Tab. 3, fig. 25—28. 

 Astrolepas LiEVis. J. E. Gray (!) Annals of Philosophy (new 



series), vol. 10, 1825. 

 Verruca cancri Americani. Ellis. Phil. Trans., vol. 50, 1758, 



PL 34, fig. 13. 



Shell steeply conical, very smooth and light ; orifice large, 

 generally exceeding half the basal diameter of the shell: 

 radii broad, smooth, only slightly depressed. 



Hah. — Mediterranean ; Gambia, West Africa ; Charlestown ; Jamaica : Hon- 

 duras ; Brazil ; Australia. Attached to Crustacea, smooth univalve shells, and 

 apparently to ships' bottoms. 



General Appearance. — Shell white, very smooth, of little specific 

 gravity, steeply conical, but not high; orifice broadly oval, polygonal, 

 very large, namely, generally exceeding half the basal diameter of the 

 shell. The summits of the compartments are usually perfectly pre- 

 served, pointed, and often a little recurved. The radii are rather 

 broad, very smooth, with their summits slightly oblique and arched : 

 they are seated only a little below the general level of the parietes. I 

 have seen one specimen rather more than one and a half inch in basal 

 diameter, but this is an unusual size ; this species not growing to so 

 large a size as the two foregoing forms. 



Structure of Shell and Radii. — The walls are here thinner than in 

 the two foregoing species ; and the basal surface of a compartment 

 rarely equals half the basal diameter of the internal cavity of the shell, 

 measured transversely to its longer axis. The radiating septa are also 

 much thinner, generally sinuous, and so finely dentated along their 

 basal edges, that the teeth can be clearly perceived only by the aid of 

 a lens. The interspaces between the septa run up to nearly the sum- 

 mits of the compartments, and hence the lightness of the whole shell. 

 The inner lamina of the parietes is here not so thick (fig. 4), and is 

 more distinct from the descending sheath than in the foregoing species. 

 The sheath is thin, like the radiating septa ; the medial loophole in 

 each compartment, for the entrance of a filament of corium, is much 

 wider than in C. testudinaria, for it is generally as wide as the bordering 

 plate on either hand ; and in not a few specimens, the medial loop- 

 hole is so wide as hardly any longer to deserve being so called, for the 

 descending sheath is reduced to mere flattened pillars or legs on the 

 sides of the sutures. Although the parietes are here not nearly so thick 

 as in the two foregoing species, yet as the radii stand but little beneath 



