!■ KID I lljOK l^KLANI;. M.-N. Kl. 



most genera, Asia and Africa each produce a characteristic genus, while 

 Europe has two. In Australia a few species have been found and were 



probably inti'oduccd by man. 



The following table contains .'ill tin- genera and their distribution:' 



Ârioii Cliicdy I'alae-Arctic. 



(icniitdldciis Kuropc. 



.liuxdciiiis From the Himalayas to China. 



Bimirya Western North-America. 



Hcnipliillia — „ - ■ 



AiKuiriiiiliis — „ — 



Propliysaoii — „ — 



llcsperarioji — „ — 



Aphallarioii — „ — 



Arioliinax — „ — 



Zacolnis — „ — 



Cryptostracon Costa Rica. 



Oopclta Africa. 



Norway has only five species, all belonging to the genus Avion. 

 PiLSBRY (1898) in particular endeavoured to elucidate the phylogeny. 

 The starting point is sought in the family Endodotitidae. With regard 

 to its geological appearance it is obvious that these feeble animals are 

 not likely to be found as fossils; nevertheless it has been possible to 

 prove the existence of several tertiary and quarternary species of An'oii. 

 The oldest are from the tertiary strata in the Basin of Mainz (Wenzel 

 191 1); and consequently this genus, which is supposed to be the \'Oungest 

 within the family, is at least of equal age. 



Genus Arion Férussac. 



Diagnosis. External characters: The shield rounded posteriorly, granulate, re- 

 spiratory aperture before the middle of its right side, close above or a little behind the genital 

 orifice. Generally a dark lateral band on each side of the back ; adults ^vith no dorsal keel 

 at the posterior end of the body. Triangular caudal cavity. 



Internal characters: Shell rudimentary, only represented by numerous calcareous 

 granulations. Tentacular and pharyngeal retractors form three separate muscles. Alimentary 

 canal like 4 whorls. Reproductive organs relatively simple (with no penis, flagellum, dart- 

 sac or digitate vaginal glands) ; lumen of ovispermatoduct continuous, and not like two sepa- 

 rated ducts. 



Introduction. Owing to several factors the genus Arion is without 

 doubt the most complicated of the family. A great many species have been 

 described {vide Heynemann 1906), and several of them are represented by 



• It is possible that the following genera should be added : 



Metostracon Mexico. 



Otoconcha New-Zealand. 



