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Sigay shells
Area 6 is basically a flat coral plain with a silty bottom with intermittent medium and large coral heads and a few scattered
coral slabs. A great deal of the area was ruined for shelling when I blasted the mooring trenches across the area to
facilitate anchoring the tankers in this mooring. The western end and seaward side still offer excellent collecting for scuba
divers.
Area 7 is nearly a continuation of Area 6 except for the greater amount of thick coral rubble. Collecting in this area is not
as good and is limited to the more common shells. The seaward edge, in about 20 fathoms, will produce many of the more rare
bivalves such as listed for Area 6.
Let me prove this accusation by discussing the variation in size of Cypraea tigris in Fiji. In The Cowry (1:3, p. 43, 1962)
F. A. Schilder has stated the average length of tigris from Fiji and Tonga as 76 mm. In The Cowry (1:5, p. 74, 1963) W.O.
Cernohorsky writes: "Every Fijian collector has a specimen of tigris from 105 mm to 110 mm...I have seen nearly 25 specimens
of tigris approaching 110 mm... From personal observations and measurements I place the mean length of C. tigris from Fiji as
about 90 mm." Let us see how this difference can be explained, and which indication is correct.
Apparently W.O. Cernohorsky fears that research workers may be led astray by only using shells from a single locality of a
region and he tells us that with some populations in Fiji, all shells are "dwarf" size. In others (especially Vatia Wharf)
all shells are "giant" size. As Mr. Cernohorsky has collected for us in a most generous way with thousands of Cypraeidae
(mostly with the animal within) from many localities all over Fiji, we base our research of Fijian shells mostly on the
specimens collected by him. In addition, Mr. Cernohorsky often provides us with the results of his own measurements of other
specimens. He told us that his maximum tigris from Vatia Wharf is 92 mm long.
We measure each shell with calipers in tenths of millimeters and get our means from each series of each locality. The
following table indicates
(1) the number of specimens,
(2) the exact locality,
(3) the length (in classes of 5 mm: 65 = 63 - 67, 70 = 68 - 72, etc.), and
(4) the mean of the length in mm.
The mean of the 7 means of population is 78, as well as the mean of all 93 specimens coming from these localities. The mean
indicated in The Cowry (1:3) was 76 instead of 78, as other sources were used there too, shells from museums, from the study
of Dr. A. Kay in The Veliger (4:1, p. 36, 1961) and shells from Tonga. But the mean of tigris from Fiji can never be 90 mm as
W.O. Cernohorsky suggested
The last two lines of the table refer to the 24 females and 33 males examined from all Fijian localities (except Vatulele
Is., where only dead shells have been collected): therefore the mean of the sum of 57 live specimens is a little higher (79
mm) than that of all 93 specimens. The difference between the average size of females (81 mm) and males (78 mm) agrees with
that observed in most other species of Cypraeidae: the average size of males is only about nine tenths of that of the females
(see The Cowry 1:4, p. 50, 1962).
The average length of shells can be approximately estimated by halving the sum of the minimum and the maximum known. As our
tigris from Fiji vary from 60 to 92 mm, the estimated mean is 76 mm, which figure rather approaches the mean size 78 mm
calculated above. This rule, however, can only be adopted for shells coming from a restricted area or at least belonging to
the same geographical race. It does not fit the tigris coming from the whole Indo-Pacific: the mean of the two extremes (44
mm measured by F.A. Schilder, 1930, in coll. Vayssière in Marseilles, and 147 mm mentioned by A. Kay, 1961) is 95 mm; it is a
far too large figure, as it is influenced by the Philippines local race schilderiana Cate (80-147 mm, estimated mean 114 mm),
while typical tigris from the vast area from East Africa to Polynesia are much smaller (44-112mm estimated mean 78 mm). The
latter figure agrees with the calculated mean of the specimens from Fiji.
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