264 MR. BRODERIP ON CLAVAGELLA. 
In the first-mentioned specimen, at the anterior or greater end of the ovate chamber, 
an insulated shelly plate has been secreted with the tubular perforations! ; that part of 
the chamber having afforded (apparently at a former period) the best communication 
with the ambient fluid: but a calcareous deposit having almost entirely cut off that 
communication, the animal appears to have been compelled to secrete a second shelly 
plate towards the anterior ventral edge of the fixed valve, where the perforation of some 
other shell (a Lithodomus probably) secured the necessary influx of the water?. Nor is 
this the only instance of the secretion of a second tubular plate which has fallen under 
my notice. 
In the last-mentioned or smaller specimen, the perforated shelly plate joins the ante- 
rior ventral edge of the fixed valve laterally, that point of the chamber being evidently 
the most practicable for communicating with the water by means of the tubules: the 
rest of the anterior edge of the fixed valve is surrounded by the coral wall. 
In Mr. Cuming’s specimen the fixed valve is continued on to the tube‘. The anterior 
edge of this valve is surrounded by the naked wall of the chamber, and the greater end 
of the chamber, or that part of it which is opposite to this anterior edge, being imprac- 
ticable, from its thickness, as a water communication, (with a small exception®, which, 
not improbably, had ceased to be available,) the animal has been driven to secrete the 
perforated shelly plates not far from the throat of the tube on either side, where the 
chambers of Petricole or Lithodomi opened a passage to the surrounding water®. Asa 
further proof of this, Mr. Owen informs me that the mantle is torn at these particular 
points. 
I feel the difficulty of laying down specific characters from the specimens belonging 
to Mr. Goldsmid and Mr. Cuming. The tubes, or siphonic sheaths, of each of them are 
broken, and nothing is left sufficiently distinct to show the form of the aperture when 
it was perfect. The valves being nearly, perhaps altogether, excluded from the light, 
colour, at best but a treacherous guide, is absent entirely. I cannot conceal from my- 
self that the shape of the chamber and of the valves, together with the comparative 
roughness or smoothness of their outer surfaces, may depend upon the greater or less 
degree of hardness of the material in which the chamber is formed. With such data, 
however, as these specimens afford, I shall endeavour to characterize them ; and if, 
hereafter, they should prove to be mere varieties, the descriptions and drawings may 
at all events assist in elucidating the natural history of the genus. 
| Plate xxxy. Fig. 1. e. 2 Ibid. Fig. 2. e. * Thid. Fig. 2. x. 
* Plate xxx. Fig. 8. d. 5 Ibid. e”. 6 Ibid. e’, e'. 
