LAMELLIBRANCHIATE CONCHIFERA. 95 
knowledge, correct. Turton says the valves of the Teredo do not correspond with the 
bore, though I think that in this case they do act as mechanical instruments. But the 
Pholas conoides is often found in hard timber, though its valves do not seem in the least 
adapted for any boring or filing. 
Certain Annelides apparently possess this power of excavation. The rocks on our coast 
are pierced by a minute worm, probably of the genus Diplotis of Montague ; it is strongly 
ciliated, but its mouth does not appear adapted for making its way into such hard sub- 
stances. By the currents excited by Vorticelle, &c. it is that the erosion noticed at the 
beaks of fresh-water bivalves takes place; the lamine at that part being soft, and 
more distant from each other. We find the valves of the Oyster, Pecten, Lutraria, &c. 
perforated by small circular apertures leading into internal cavities. Dr. Buckland 
showed this to depend upon the action of a zoophyte, which Prof. Grant has particularly 
examined, and named Cliona celata. Dr. Buckland considers the holes to be formed by 
little borers which the polypes possess ; these, however, do not exist, and I believe the 
phenomenon to be caused by the action of the cilia of the animal. 
Freminville, Nilsson, Beudant, Stark, and others, agitate the question as to whether 
freshwater Mollusca can live in salt water, and vice versd. To ascertain whether respi- 
ration could go on in the Lamellibranchiata, the habitat being so changed, I took a 
portion of the branchie of a Mactra, and placed it in fresh water for one minute; the 
cilia, strongly in action before the experiment, stopped in their vibration, and could not 
be restored by immersion in sea water. Five grains of common salt were added to an 
ounce of fresh water, and a portion of the branchie placed in the solution, upon which the 
vibration ceased. In a solution of ten grains of common salt to an ounce of fresh water, 
the vibration was continued, as it was also in a solution of twenty grains to the ounce. 
In a stronger solution it shortly stopped. After a short immersion in the strong fluid, 
it was restored by the second solution; but a Mactra, of which the branchie were 
exposed for fifteen minutes to the action of fresh water, did not recover itself though 
returned to its native element. Sea water, or a solution of even two grains of common 
salt in an ounce of fresh water, immediately stopped vibration in fresh-water Mollusca. 
It would seem from this, that the capacity of bearing a change as to the freshness or 
saltness of the water is very limited in these animals ; for if the cilia cease to vibrate, 
respiration must stop, as well as the collection of the nutrient particles from the water. 
Perhaps the inhabitants of estuaries are best adapted to bear a change in this respect ; 
but what Nilsson and Freminville state respecting the Anodonte, &c. being found in 
company with Telling, &c. appears very debateable ; the circumstance probably arose 
at the mouth of a river. The Cardia, Mactre, Amphidesme, &c. found in salt marshes, 
die when the water becomes concentrated by evaporation, or when it loses its saltness 
by being mixed with fresh. The Mytili found in fresh-water docks are probably fresh- 
water species brought from foreign rivers attached to vessels, and which have probably 
survived their voyage by having kept their valves constantly closed accurately. 
VOL. I1,—PART II. Oy) 
