20 Red Sea Shells. 



some rare eases it is even used as a punt pole by the ingenious 

 mollusc ; which by dint of its muscles can stiffen the limb as well 

 as contract it, and so help itself forwards by pressing against the 

 sand from behind. But all limas are not thus active. Many of 

 them spin a byssus and moor themselves to a rock when they grow 

 old ; others make an artificial burrow of coral fragments, and hide 

 themselves as in a nest. I do not know why this should be so, but 

 the habit is not peculiar to shell fish. We often meet people, who, 

 as they get on in life, grow tired of moving, and find it very com- 

 fortable to bury themselves in a burrow of outworn prejudices, 

 where they can close up both openings, or to spin a theory and 

 insist upon sticking by that to one spot which after all may be a 

 very barren one. Let us take warning b}' the lima. 



I selected the clam to illustrate the strength and size attained 

 by some of the molluscs. The spider shell and cowrie as instances 

 of the marvellous changes to which their forms are subject, 

 and I have described the lima in order to show how beautiful and 

 ingenious are their methods of locomotion. Here is another shell 

 which if it illustrates nothing in particular may at least lay claim 

 to oddity. It is not new to the Society. Mr. Farrar exhibited 

 one of a different species a few weeks back, nor can I lay claim to 

 have picked up this specimen myself, although I found the 

 fragments of one three times the size, and which, had it been 

 perfect, would have been the most valuable shell in my collection. 

 Perhaps you will be surprised when I tell you that this shell is a 

 bivalve, and in this consists its oddity. If you will examine it 

 closely, you will perceive at the lower end of this long tube the 

 umbones of a very tiny shell, which is in fact buried in it, and 

 looks much more like a subsequent accretion to the cylinder than 

 the source of its growth. What can so insignificant a creature 

 want of so enormous a tube. As it grew in size it seems to have 

 discovered the attractions of a large chimney corner, and instead 

 of enlarging the valves of its shell like an ordinary mollusc, to 

 have determined to " go out" in a novel kind of architecture. The 

 lower end of the tube, you see, is closed by a perforated disc like 

 the rose of a watering-pot, whence the Latin name of the creature 

 " Aspergillum" and the French " Arrosoir." It belongs to the 

 family of Gastrochajnidae or gaper shells, so called because their 

 valves when closed do not unite completely, but leave a moderately 

 wide aperture. They are all burrowers, and breathe when buried 

 in sand or rock by means of long retractile siphons, which pro- 

 trude through the aperture to the surface. In the common Mya 

 these siphons are unprotected by any tube. Here is a specimen, 

 in which the siphons are shrivelled up with age, that in their live 

 state would have been capable of considerable extension at the 



