403 



which exceeds it in number in other circumpolar regions has in Green- 

 land displaced or at any rate replaced it altogether. 



If, however, Limax agrestis, notwithstanding the advantage which 

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

 beaten in the struggle for existence in circumpolar districts by Arioti 

 hortensis of about the same size but of such different colour in other 

 districts, if not in the North 3, as not only to have been called fuscus 

 and suhfuscus^ but even to have been confounded with the true Avion 

 (iter from which indeed it is mainly distinguished by its more mesially 

 placed respiratory orifice and its small size, it surpasses Arioti liortensis 

 (see Schrenk, Amurland, II. 1S69. p. 690—693; Middendorff, 

 Sibirische Reise, II. 1851. p. 424.) in more southern latitudes. 



Middendorff indeed expressly says 1. c. »In Sibirien traf ich 

 diesen Limax [Arion hortensis] nicht , sondern nur einen einzigen 

 kleinen Limax im Stanowoj-Gebirge, welcher dem Limax agrestis L. 

 recht ähnlich sah«, but this absence from Siberia, to which F. Schmid t's 

 silence as to its presence bears some testimony, may be paralleled by 

 the similar absence oï Paluditia vivipat'a (Middendorff, 1. c. p. 426) 

 and of Crayfishes from the Siberian River Basins (see Huxley on 

 Crayfishes, p. 305), and when, as in these two cases, compared with 

 the facts of distribution elsewhere does not disprove a circumpolar 

 character. 



Gerstfeldt, Mém. Sav. Étrang. II. St. Pétersbourg, 1859. p. 515 

 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 Arieti ater. Their 

 small size may justify us in supposing them to have been Arion liortensis^ 

 and the bad state of preservation in which they were and which makes 

 Gerstfeldt himself speak doubtfully of his identification p. 535 (31), 

 makes 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 oî Limax agrestis. An illustration of the paucity and 

 rarity oî 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 Jenisei, Mém. Acad. St. Pétersb. 1872. p. 48 as to this emi- 

 nently social Mollusc. »In einem faulen Treibholzstamme auf der großen 



3 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, some- 

 times grey or greenish grey». Lovell Reeves, British Land and Freshwater Molluscs, 

 p. 1 1. In the Amoorland it is »graugelblich« with three stripes, one dorsal around two 

 lateral narrower ones; whilst its rival the Limax agrestis is described as »hell 

 bräunlich- oder bläulich-grün«. See Schrenck, 1. c. 



