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Show 248 MESSES. COLLINGE AND GODWIN-AUSTEN ON [Mar. 19, M. pollonerai there is a tendency to change, as shown in the twisted amatorial organ and the form of the calc-sac. V. SUMMAEY AND CONCLUSION. The chief features on which we would base the specific distinctness of the afore-mentioned new species are as follows :- 1. DAMAYANTIA SMITHI. D. dilecta, Issel, at present being known only from external features, we would point out that it differs from our species externally in the form and size of the mantle-lobes, the lesser development of the left lobe, and presumably in having a smaller and less solid shell than that possessed by D. smithi. 2. MICEOPAEMAEION POLLONEBAI. The form, size, &c. of the penis and calc-sac are quite sufficient to separate this species from any already described. The densely convoluted common-duct and the sharp coil in the amatorial organ are also characteristic of this species. 3. MICEOPAEMAEION SIMEOTHI. M. strubelli, Simr., is undoubtedly the nearest ally to M. simrothi. For purposes of comparison we have reproduced Simroth's figure (7. tab. viii. fig. 12) on fig. 39, and it will be seen that our new species differs from the former in the following details:- a. The larger and more perfect shell. b. The different form of the penis, albumen-gland, and hermaphrodite gland. c. The almost straight common duct (prostate and oviduct). d. The large amatorial organ. e. Less important differences in the form of the flagellum, vagina, and free oviduct. There is, as one might expect, considerable similarity in these Bornean slug-like forms. This is shown in so many important organs, wherein they differ from the slugs of the Indian region, notably in the form of the dart, short sessile receptaculum seminis, and differently formed male organs, which would materially alter the form of the spermatophore. But perhaps the most interesting result of the examination of these slug-like molluscs is their similitude internally to the similar parts of shell-bearing species which inhabit the same island of Borneo. A reference to the figures and description of the genera Everettia and Dyakia (2) will show that the calcareous dart peculiar to Microparmarion occurs in both of these genera, while the odontophore of Damayantia smithi agrees with that of Dyakia in a remarkable manner. It seems to us that there can be little doubt but that the sluglike forms of Borneo have the same close relationship to the shell-bearing molluscs among which they are now found living, as the |