NEW YORK SHELL CLUB _ NOt?Es 
Page 4 March 1978 No. 240 
it is reasonably certain that the ducks had made a meal of Melano- 
i shi h they had been: they 
ides. It was astonishing to see how thoroug : 
rae eae not missed a single snail, from minute newly hatched 
baby to mature adult. At least I could discover none after a long 
search. 5 a * 
This event is interesting from two points of view. (First, as is 
well known, Melanoides tuberculatus is an Asian snail that has in 
vaded Florida and other southern states. Usually such an introduc- 
tion of an alien species turns out to be harmful to the local flora 
or fauna, since the intruders increase amazingly in numbers. There 
is no native biological control to keep their numbers down. However, 
here we find native wild ducks serving as an active and very effec- 
tive control. In addition, the advent of Melanoides may prove es- 
pecially beneficial for the ducks. EG provides a rich new Source of 
food which might cause the duck populations to flourish. This for 
the first comment. 
Second: Dr. Harold Murray of Trinity University in Houston, Texas, 
has recently been studying a disease of the nictitating (tear pro- 
ducing) membrane of the eyes of wild ducks in the Houston Zoo. He 
has found convincing evidence that the disease is caused by a 
trypanosome, whose vector is none other than Melanoides. Hence, if 
I may be permitted a dramatic observation, there is here a mini-war 
of the disease bearer against the eyes of its victim, and the victim 
against its disease bearer. Who can win? 
SEA SHELL 'TREE RINGS' FROM THE SEA SHELF 
Just as tree rings record climatic conditions on land, a bivalve mol- 
luse named Arctica islandica has been found to record conditions of 
the shallow ocean by variation in the width of annual bands on its 
hinge plate and outer shell layer. Ida Thompson and Douglas S. Jones 
of Princeton University are studying this banding with methodology 
borrowed from tree-ring research. They have confirmed that the bands 
are annual, that they vary in width and that shells with up to 150 
bands are available. Their working hypothesis is that minimum winter 
temperature is the most important factor controlling the width of 
the annual bands. Species of Arctica are not uncommon as fossils, 
they say. Sectioning of the shell of one species from Alberta re- 
veals beautifully preserved banding. "Eventually," Thompson and 
Jones suggest, " - iti ‘ 
oxen eRe Tasik paleo-ocean conditions may be read from fossil Arc- 
SCIENCE NEWS, Vol. 112, Nov. 26, 1977 
(Contributed by Henry S. Gordon.) 

The following article appeared in NYSC 
NOTES No. ° i 
from PACIFIC NORTHWEST SHELL NEWS, Vol. II, Noe D Ren ngeae 
READING SHELLS 
by Dr. H. C. McMillin 
S F 
cane Studying the razor clams of the west coast and 
Petes Pee ee e making of logical regulations for the legal con- 
ery. The biological basis of control is age of clams 

