1922. No. 5. ARIONIDAE OF NORWAY. 



a great number of varieties. Further, a peculiar feature of this genus is 

 the tendency to continuous variations, a fact which is likely to appear 111 

 the present paper. Therefore, this group still offers many systematical 

 problems, and in his synopsis Hevnemann exclaims : "Wenn sich doch ein 

 Malakologe der Gattung Arioii annehmen wollte; sie ist die schwierigste 

 von allen uns naheliegenden". As it is often of importance to study the 

 lixing animal, in my opinion the genus should be revised in all countries 

 within the limits of its distribution. It will then be time to write a satis- 

 factory monograph of the genus Arion, and he who overcomes the 

 difficulties of applying genetic methods to the group will be sure to 

 find interesting results, to discover laws where now we have only iso- 

 lated facts. 



Historical systematics. Before Linné slugs were included in the 

 term Liiiiax or Cochlea iiuda (Asiaa^ — slug). When Linné had given 

 his sanction to the name Lima.x, it was used collectively for a long time, 

 even as late as by Joachim Friele (Norske Land- og Ferskvands-Mollusker, 

 1853). Long before, in 18 19, Férussac in his Histoire des Mollusques had 

 separated the genus Arioii from Liiiiax ('Apwov, either after a person in 

 Greek m3^thology, a poet and musician from the Isle of Lesbos, or ironically 

 after a mythological horse famous for its speed). Later on the genera 

 were found to belong to two distinct families.' 



At various times the species of Ario/i have been placed in sub-genera, 

 all of which for the present time should only be of historical interest. Thus 

 Moquin-Tandon distinguished between the sub-genera Lochea (type Arioii 

 ater) and Prolcpis (smaller species), the former characterized by its rudi- 

 mentary shell in the shape of loose calcareous granulations, in the latter 

 as a coherent membrane. As a principle of division this variable character 

 was a complete failure, although the names were used as genetical terms 

 by Malm (1870t. — The sub-genus Carinella of Mabille (type Arion circum- 

 scriptits) was given to forms with the dorsal keel especially conspicuous 

 in the 3'oung. But this term too, is never used. 



SiMROTH divided the genus in the Moiiatriidac, with undivided atrium 

 genitale, and the Diatriidae, with an upper and lower part separated by a 

 transverse constriction. Later on it was found that this character varies 

 in the same species, and therefore these groups cannot be sustained. 

 To this day only the name Ariitiiadtts — an original generic name estab- 

 lished by Lessona — has been applied to some small species that were 

 considered to form a natural unity, a sub-genus ; as shown under Arion 

 intermedins, however, this is not the case. 



I am inclined to believe that the most natural arrangement of the 

 species is that of Collixge (1897), at least at the present stage of our 



1 The family Arionidac was established in Turton's : Description of some new British 

 shells, 1840. 



