44 TROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



investigation of the present genus has been made. At present the 

 connection with ILijalimax seems to be the more intimate ; but possibly 

 we have only to deal with the results of convergence. The SuccinciduB, 

 which show great predilection for moisture, in spreading out from a 

 northern centre across the Equator would seem to have given rise to 

 several forms of slugs. Mijalimax on the one side, Ilomalonyx and Neo- 

 liyalimax on the other, would be southern outposts. This hypothesis 

 would be in accordance with the theory put forward by Dr. Haacke 

 and myself, that the greatest number of groups of terrestrial animals 

 originate in those parts of the world where the continuity of land 

 is greatest. An entirely different conclusion would result from the 

 c\idence of a nearer relationship between Hyalimax and Neoliyalimax 

 than between the latter and Ilomalonyx. It would accord with the 

 idea of an old Jurassic land connection between South America and 

 Africa. Hyalimax, indeed, is not African, but restricted to the Indian 

 region ; there is, however, a form from Kilimaudjaro described by 

 Yon Martens as Parmarion Kerdenii (4), which is likely to be nearly 

 allied thereto. I merely wish to show by these remarks that a more 

 intimate knowledge of these animals would throw light upon questions 

 of very general interest. 



(b) Its relation to the Athiracoplioridce. — Succincoid slugs, such 

 as Ilyalimax and Neohyalimax, are in a certain sense of general 

 systematic importance. Placing the Succineidiic at the end of the 

 quadritcntaculate Stylommatophora, the textbooks include the rest 

 as Bitentaculata, in the families Athoracophoridfc, Vaginulidae, 

 Oncidiidte, overlooking the disappearance of the smaller tentacles 

 in some small Pupida?, etc. I group these three families under 

 IMesommatophora, taking the Athoracophoridae as a transitional form. 

 Fischer joins the Athoracophorida3 to the Succineida3, and groups 

 together the Vaginulidoe and Oncidiida) as Ditremata. Pclseneer 

 places the Succineida), with Atlioracophorus, at one end of the 

 Stylommatophora, and the Vaginulidne and Oucidiidae at the other. 

 I should not like to do so. The intimate fusion of the pleuro-visceral 

 ganglia demonstrates the derived character of the Succineidte ; on the 

 other hand, the total absence of a columellar muscle is an important 

 point of agreement between the Athoracophoridaj and the Ditremata, 

 the lack of a common atrium genitale in the Succineidte forming a 

 transition to the state of separate genital openings which obtains in the 

 Ditremata. Atopos would bo the intermediate form. The relationship 

 between the Succineidie and the Athoracophorida? has been founded 

 upon the similarity of their jaws and radula3. Perhaps the columellar 

 muscle of Neohyalimax, in which the retractors of the tentacles attain 

 a certain degree of independence, may prove another point of affinity. 

 Nevertheless, the pallial organs, even though imperfectly known, 

 exhibit a wide divergence. For this reason I should prefer the 

 arrangement given by Fischer, i.e. Succineidie, Athoracophoridai, 

 yaginulida3, Oncidiidiie, with the modification that each of the three 

 latter families is to be looked upon as independent. 



