298 THE ZOOLOGIST. 
much value, and it all has to be knocked down to ensure a crop 
of good quality next season, whether it be white or black. 
Mr. Layard says that his experience is—if I understand him 
rightly—that the first gathering of a “crop” (sic) is white, the 
second black and feathery, and the third mixed with grass, &c. 
In this country, at all events, there is nothing of this sort; white 
nest is always white nest through all its seasons and gatherings, 
and black nest the same. The nests mixed with grass, &c., that 
Mr. Layard describes do exist, however. I have seen some that 
were brought from Palawan, which is so much mixed with grass 
and moss as to be valueless, but it is always the same, and though 
collectors were got over, and the caves thoroughly cleaned, with 
the hope of getting better quality at the next gathering, it was 
just the same, mixed with grass and moss as before. May not 
Mr. Layard have mistaken nest taken from different localities for 
successive collections from the same cave ? 
With regard to the material from which the nests are made, 
I regard the Alge theory with great doubt. The natives say the 
birds skim up froth or scum from the water, and use it as the 
material. I myself think it is simply a natural secretion of the 
birds themselves. [But see Mr. G. Murray’s note, p. 147.—Ep.] 
There are still a great many points in connection with these 
Swiftlets that are very obscure, and which I have abstained from 
touching upon, but will endeavour to clear up as time goes on. 
THE MOLLUSCA OF THE COUNTIES OF KENT, SURREY 
AND MIDDLESEX. 
By T. D. A. CockERrELu. 
(Continued from p. 180.) 
LIMNZID2. 
Planorbis lineatus.—Very local, more common in East Kent 
than elsewhere. In Surrey it is found on Barnes Common ; 
Middlesex and W. Kent (W. D. Roebuck). Knole Park (Smith). 
Var. albina.—Near Deal (Mrs. Fitzgerald). 
P. nitidus.—Ebbsfleet and Minster (S. C. C.) ; Chislehurst ; 
Kew; Fulham; River Lea at Tottenham (C. Ashford). 
