Yol. 68.] ON" MOLLirsCA. PEOM THE AECTIC BED. 235 



Notes on the Species. 

 Arion sp. 



There are several granules representing the internal shell of this 

 genus, but it is quite impossible to ascribe them to a given species. 

 The northern limit of Avion is the isotherm of 8° C, but on the 

 Alps its vertical limit is the isotherm of 3° to 4° C. It may here be 

 observed that the isotherms quoted in this note are those for July. 



LiMAx ARBOEiTM Bouch. -Chant. 



This species is common, but all the examples are dwarfed. Its 

 northern limit is Iceland, lat. 66° 30' N., with an isotherm of 8° C. ; 

 while in both Norway and Sweden its limit is the isotherm of 

 8° to 10° C. In the Alps its vertical range is the isotherm of 10° C. 



Agriolmax LiEvis (Miill.). 



There are only four examples of the internal shell of this species. 

 Its northern limit in Europe is the isotherm of 14° C. ; but, if 

 A. hyperhorea West is only a variety of Icevis, as has been suggested, 

 it ranges in Asia as far as the isotherm of 10° to 12° C. 



Sphyradium columella (G. v. Mts.). (PI. XYII, figs. ^ a &, b h.) 



Abundant. This is an extremely interesting species, and one 

 over which there has been considerable confusion. 



It is the custom in this country to consider it as a variety of 

 Sph, edentulum (Drap.), and as not uncommon in a living state ; 

 but the shells to which the name columella is applied by British 

 authorities are very different from the true columella, and are in 

 fact an elongated form of edentulum. 



The species columella (vera) does not occur in a living state in 

 these islands. It is a high Alpine and Arctic species inhabiting 

 Norway, Sweden, Einland, and the Alps. Its northern limit is the 

 isotherm of 8° to 10° C, while its vertical limit in the Alps is 

 the isotherm of 6° to 8° C. In these islands it is only known 

 from the Pleistocene of Barnwell (Cambridgeshire) and Copford 

 (Essex). It is a common fossil in the German loess. 



It is interesting to note that a similar disposition occurs in the 

 Nearctic region. There, as in Europe, Sph. edentulum (Drap.) is a 

 widely distributed species, but an elongated form, Sp)h. alticola Ing., 

 occurs living at a height of 8000 to 9000 feet in Colorado ; and it 

 also occurs as a fossil in the Mississippi 'loess.' Whether the 

 species alticola is identical with columella we cannot say, for we 

 have been unable to see an authentic specimen of Spli. alticola. 



Vertigo parcedentata (A. Braun). (PL XYII, figs. Qa & Qh.) 



Seven examples of this species were detected. They belong to 

 the variety genesii, Gred., which is the edentulous form oi p>arce- 

 dentata. This is a rare form in a living state, being only known 



Q. J. G. S. No. 270. s 



