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Nautilus
Nautilus The difference between the Seychelles (mean 4.3), East Africa (5.0) and South Africa (7.7) is obvious. Therefore there is not only a local tendency of variation, but also a regional one: one is justified to summarize adjacent localities and to calculate an average class of marking in each region:
Kowie-Pondo 7.9, Natal 7.3, Mozambique 6.5, East Africa 5.0,
Madagascar 6.5, Mascarenes 5.1, Seychelles 4.3, Gulf of Aden 6.3,
Ceylon 5.8, West Sumatra 5.6, South Java 6.1, N. W. Australia 4.9,
S. W. Australia 5.7, East Australia 6.0, New Caledonia 4.5, Fiji-Samoa 4.8,
Solomon Is. 5.2, Bismarck Arch. 5.6, Moluccas 5.1, Java Sea 5.8,
Philippines 5.6, Taiwan-Japan 5.6, Bonin-Guam 6.0, Caroline Is. 4.2,
Marshall Is. 3.9, Gilbert Is. 3.7, Tabiti-Tuamotu 4.0, Line Is. 3.4,
Philippine Is. 3.7, Midway Is. 4.6.
The mean of these 30 regions is class 5.3 (dotted area very slightly exceeding the speckled one). If one replaces the five intervals 3.4-4.3, 4.4-5.3, 5.4-6.3, 6.4-7.3, 7.4-7.9 by visual signs and plots them into a map, one will observe great geographical tendencies: 1. in the centers of oceans, especially from the Tuamotu Is. to Philippines and Micronesia, and in a smaller area around the Seychelles, the brown dots are least developed; 2. they pass into the subcontinental regions from Japan to Australia and Ceylon as well as along the East coast of Africa, in which the brown dots slightly exceed the white specks; 3. in South Africa there is a center of maximum development of brown dots, which character fades in the adjacent regions of Mozambique and Madagascar.
This study on the dorsal markings of E. helvola shows that careful registration of such superficial and variable characters bring to light interesting ways of geographical evolution.
Nautilus We have just concluded a catalogue of the sea shells (Cypraeidae) and three allied families ("semi-sea shells") which will be published in Brussels in 1970. It contains a bibliography of 3650 books and pamphlets published on this subject till December, 1968, and 3720 names proposed for various fossil and living taxa. But the 3359 names of species level include many synonyms and individual varieties so that the number of real species, plus well defined stratigraphical or geographical subspecies, becomes exactly 1300, almost two-thirds of which are fossils. The ten subfamilies differ with regard to the number of these taxa of species level worth to mention, both absolutely and with regard to the percentage of fossil ancestors and living successors. This fact may be learned by the following table [at left]:
The true sea shells (Cypraeidae) comprise about one half (53 percent) of the total sum 1300, but the percentage of fossils (62 percent) is almost identical to that of all 1300 sea shells and semi-sea shells (64 percent).
Malacologists will welcome the illustration of the table in a diagram:
One will observe that in 4 groups of different size (Cypracinae, Erosariinae, Triviinae, Erroneinae) the number of now known fossil species is about identical with that of living ones; in other groups (Eratoinae, Bernayinae, Eocypraeinae, Cypraediinae) the fossils are prevalent, while in groups with fragile shells (Pediculariinae, Ovulinae) the living ones seem to be more numerous than discovered ancestors.
Here is a follow up on the story, "A Search for Cypraea isabellamexicana, "Sean Raynon Sabado, Vol. xiii, no. 9, July, 1965.
The same members of that unsuccessful three week search for the rarest of eastern Pacific sea shells made another diving, shell bunting trip together in March, 1970. This time Commander Norman Currin, Billee Dilworth, and Twila Bratcher, with aqua-lung instead of hookah gear, had no specific shell as an object of their search. Instead of Baja California, their diving locations were the west coast of Mexico from Mazatlán to south of Puerto Vallarta.
The best finds of the trip were a pair of Cypraea isabellamexicana for each of the three collectors. Found on different days and at different depths, Norman Carrin's pair were under adjacent rocks, while Billee Dilworth's and Twila Bratcher's pairs each were under single rocks.
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