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Show 1891.J LAND-SHELLS FROM BORNEO. 23 obtained by Colonel Beddome in Travancore. Sitala is another genus having a similar distribution, and one section of it (represented by the peculiar little shells S. tricarinata and S. subbilirata of the Nilghiri and Andaman Islands respectively) finds a representative species in Borneo in Sitala kusana. When the intervening countries and islands come to be better known, other allied forms will no doubt be found. The closer the external characters of the animal are looked at, and the more an attempt is made to combine these with the form of the shell for the purpose of generic classification, the greater are the difficulties met with. Dr. von Martens found this so much the case when he took up the Land-shells of Eastern Asia, that he fell back on to the shell alone. If, however, we go further and take the internal anatomy, especially the points of difference in the reproductive and other organs, and the odontophore, which has been so well done by Professor Semper in the same region, we do find some well-marked differences, and these we discover have but little bearing on the form of the shell, which may be considered as of secondary importance. It is to be expected that modification of the internal structure of the animal is brought about much more slowly than change in the shelly covering, and that it is consequently far more persistent. The first is a combination of many different organs, a change in one affecting all the others, while the shell is a single structure merely secreted by the mantle, and affected rapidly by change of climatic conditions and the nature of the rock on which the animal lives. When such a sounder system of classification has been thoroughly worked out, we shall be able to trace with some degree of exactness the areas over which certain genera of Land-Mollusca extend. Then noting how such areas have been affected by the more recent geological changes leading up to the present outlines of the land and the intervening seas, we may be enabled to contemplate and draw some conclusions as to how far present distribution has been dependent on and connected with such changes. In the descriptions of the species which follow, I have attempted to show how very different are details of the anatomy of the Bornean Helices when compared with those of very similar-looking shells of the Indian region. Fam. ZONITIDiE. Vaginula hasselti, v. Martens, Preuss. Exped. Ost-Asien, Land-schneck. p. 176, t. v. figs. 2, 4 (1867); Fisch. Nouv. Arch, du Mus. vii. p. 158 (1871). Hob. Borneo, near Benkajang. Vaginula bleekeri, Keferst. Zeitschr. f. wiss. Zool. 1865, p. 118, t. ix. figs. 1, 2 ; v. Martens, Preuss. Exped. Ost-Asien, Land-schneck. p. 177 (1867) ; Fisch. Nouv. Arch, du Mus. vii. p. 161 (1871). Hab. Sarawak (Doria and Beccari). |