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SECTION B.

Anthropology, Ethnology, Bacteriology, Botany,

Geography, Geology, Mineralogy,

and Zoology.

Section B.

CAPT. THOS. QUENTRAL, F.G.S., M.I. Mech. E., was President of this Section, but did not submit an Official Address for publication.

SOUTH AFRICAN TORTOISES.

By J. E. DUERDEN, PH.D., A.R.C.S.

Professor of Zoology, Rhodes University College; Keeper of Zoological Department, Albany Museum.

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In South Africa there occurs an extremely well-defined group of tortoises, all the species of which are referred to by Prof. G. A. Boulenger, in the British Museum Catalogue of Chelonians, as "allied to Testudo geometrica." They are readily distinguished from other tortoises by having a black or dark brown carapace, each shield of which is conical with bright yellow rays extending from

the central areola. The original type, Testudo geometrica, is a wellknown Linnean species, found in the Cape District.

With the extended exploration of South Africa, more and more of the geometrica-like tortoises have been discovered, so that at the present time the group comprises ten described species:-1, Testudo geometrica, Linneus, 1766; 2, T. oculifera, Kuhl, 1820; 3, T. tentoria, Bell, 1828; 4, T. verre auxii, Smith, 1839; 5, T. trimeni, Boulenger, 1886; 6, T. smithii, Boulenger, 1886; 7, T. fiskii, Boulenger, 1886; 8, T. strauchi, Lidth de Jeude, 1893; 9, T. seimundi, Boulenger, 1903; 10, T. boettgeri, Siebenrock, 1904. It is a significant fact that five of the species have been founded on single specimens, and in not more than two or three instances has a large number of specimens been available for determining the limits of variation or the relationship of the species to others previously described.

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The fact that so many species of a clearly defined group occur in one region, all acknowledged to be very closely allied, suggested that a thorough study of the geometrica-tortoises on the spot might yield results of importance as regards the origin of the variations, their degree of distinctness, and their relationships; in other words, might illustrate in some way the method of evolution of the different species. For the prosecution of such a study large numbers of specimens are required, obtained from as many different sources possible. From efforts already made, about 300 examples have been procured from various localities in South Africa. The collection can probably be regarded as fairly representative of the different types of the geometrica-group, though a perfect study of this kind. would require that every individual specimen, living and dead, should be compared, and, where possible, the results stated in statistical terms. For specimens received acknowledgments are due to the Director of the South African Museum, Cape Town, of the Natal Government Museum, and of the King William's Town Museum, as well as to numerous contributors throughout South Africa, among whom Mr. S. C. Cronwright Schreiner, M.L.A., deserves special mention.

During the progress of the work, as more and more specimens became available for study, the more difficult became the task of arranging them systematically among the recognized species, and the more evidence was accumulated as to the close relationship of the species so-called, thereby confirming the idea of their common genetic nature. Moreover, it soon became manifest that the different series include some remarkable transitional forms, and also that characters incipient or fluctuating in one group of specimens were well developed or fixed in other groups. In every direction evidence was afforded of determinate variation or variation along definite lines (orthogenesis) in contrast with indeterminate or discontinuous variation (mutation).

Though the occurrence of transitional series of organisms is by no means unfamiliar to the zoologist, yet it is very desirable that they should all be thoroughly worked out with the object of discovering what particular new light they may shed upon the all-important

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