574 ON THE GEOaRAPHlCAL DISTRIBUTION 



its coloration might be supposed to have been likely to give it, is 

 beaten in the struggle for existence in circumpolar districts by 

 ArioTt /lortensis, of about the same size, but of such different colour 

 in other districts, if not in the North \ as not only to have been 

 called /usc?is and sub-fuscuSj but even to have been confounded with 

 the true Arion ater (from which, indeed, it is mainly distinguished 

 by its more mesially placed respiratory orifice and its small size), 

 it surpasses Arion hortensis ^ in more southern latitudes. 



Middendorff indeed expressly says, 1. c. : ' In Siberien traf ich 

 diesen Limax [Arion Jiortensis) nicht, sondern nur einen einzigen 

 kleinen Limax in Starowoj Gebirge, welcher dem Limax agrestis^ L. 

 recht ahnlich sehe.' But this absence from Siberia, to which F. 

 Schmidt's silence as to its presence bears some testimony, may be 

 paralleled by the similar absence of PalucUna vivipara (Middendorff, 

 I.e., p. 436) and of crayfishes from the Siberian river basins^, and, 

 as in those two cases, when compared with the facts of a distribution 

 elsewhere does not disprove a circumpolar character. 



Gerstfeldt, 'Mem. Sav. Etrang. St. Petersbourg,' 1859, 515 (11), 

 refers to some few, small, ill-preserved specimens, ^einige wenige 

 kleine und schlecht erhaltene Exemplare ' of slugs from Irkutsk 

 and Wilni and from the Amur, and speaks of them under the name 

 Arion ater. Their small size may justify us in supposing them to 

 have been Arion hortensis ; and the bad state of preservation in 

 which they were, and which makes Gerstfeldt himself speak doubt- 

 fully of his identification, p. ^'>^^ (3^)* niakes this note of their 

 presence less authoritative than it otherwise would have been, and 

 has caused Schrenk to suggest that they were in reality specimens 

 of Limax agrestis. 



An illustration of the paucity and rarity of Limax agrestis in 

 circumpolar regions is furnished by the entry made by Friedrich. 

 Schmidt in his list of Animals from the Region of the Lower 



^ Even in England, where the Arion hortensis is often of a ' deep blue-black,' and 

 is, I suspect, the ' Black Jack * of agriculturists, it is not rarely * yellowish,' sometimes 

 •gray or greenish-gray ' (Lovell Reeve's 'British Land and Freshwater Molluscs, p. 1 1). 

 In Amoorland it is * graugelbllch,' with three stripes, one dorsal and two lateral 

 narrower ones ; whilst its rival the Limax agrestis is described as ' hell-braunlich- 

 oder bliiulich-grau.* See Schrenk, 1. c. 



2 See Schrenk, ^Amurlande,' ii. 690-693, 1869; Middendorff, 'Sibirische Reise,' 

 ii. p. 424, 1 85 1. 



» See Huxley, ' On Crayfishes,' p. 305. 



