INTRODUCTION. 



The Gli(.ii<rui(i' were fovmerly widely spread over the European region, 

 ami also lived in this country, and though still meagrely represented in 

 Southern lilarope, are now practically expelled to Central America and the 

 West Indies, where the Tuutropolis of the genus is now located, and 

 where living species have been found scarcely distinguishable from the 

 fossilized shells of our Oligocene strata. 



It has boon suggested tliat Limax and Mihw have their immediate 

 derivation from HijnUn'ia, but it is by no means certain that this is the 

 case with JSlUa.r, Prof. Babor remarking on their strong affinity with 

 Hdlr. The more distant ancestors cannot be indicated with any approach 

 to precision, but it is certain that they would possess a more substantial 

 shell than the ITijuIUiIk now possess. The trne Liiiinrichv retain the soft 

 and supple body, and the degenerate shell, though reduced to a flat and 

 almost un-nncleated calcareous plate buried beneath the mautle, is still 

 p)resent. The group is almost restricted to the Palajarctic zune, the most 

 advanced and recently evolved species occupying a compact and compara- 

 tively restricted area, while the more ancient and primitive species have 

 achieved a wider dispersal, but have been more or less completely expelled 

 from the most active evolutionary region, or compelled to resort to and 

 become isolated in undesirable spots. 



The ArioiiiJw are believed to have descended from Endodontoid 

 ancestors, a group which, though world-wide in distribution, has now 

 withdrawn its headquarters or metropolis to the islauds of the Pacific 

 Ocean. 



The typical genus Ar'mn is naturally restricted to the Palearctic region, 

 extending from Portugal to Siberia. It displays the practical completion 

 of the process of shell degeneration, and will in all probability be followed 

 by a gradual calcification of the outer iutegument, as a dense deposition of 

 lime particles and sjiicula within its substance has been already initiated, 

 and in Arion (iter has imparted a certain stiffness and rigidity to the 

 body and to its movements; this being the first stage in the slow evolution 

 of another complete shelly protection. That tlii.s, or a similar process, has 

 probably occurred in the past, is demonstrated by the vestiges still present 

 in certain species of moUusks of previously existent primary or primary 

 and secondary sliells or "Protoconchs," wliich are the last remaining evi- 

 dences of move perfect shells once jiossessed and successively lost, but 

 which had undergone, untold a.ges ago, cycles of development and degenera- 

 tion similar to that many .shells are undergoing at the present day. 



The genus (u'lniut/nriis is apparently now confined to Western pjurope, 

 and to Ihe south-^vest corner of Ireland, which is a last i'oothold fur many 

 jilants and other forms of life on the verge of extinction in this country. 



