248 MESSRS. COLLIXGE AND GODWIN-AUSTEN ON [Mav. 19, 



M. pollonerai there is a tendency to change, as shown in the twisted 

 amatorial organ and the form of the calc-sac. 



V. SUMMABT AND CoNCLTJSION. 



The chief features on which we would hase the specific dis- 

 tinctness 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. MiCROPAEMABION POLLONEEAI. 



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. MlCROPABMABION SIMKOTHI. 



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 herma- 



phrodite 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 Dyalcia (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 slug- 

 like forms of Borneo have the same close relationship to the shell- 

 bearing molluscs among which they are now found living, as the 



