306 HELICIGONA. 



Shell globose or globose-depressed, with convex or conoidal spire, 

 and narrow or closed umbilicus ; surface shining, spirally striated, 

 usually with a supraperipheral band, and mottled or dark coloring. 

 Aperture round-lunate, oblique, toothless ; lip expanded and white- 

 lipped, reflexed at columellar insertion. Type H. arbustorum L., 

 pi. 43, fig. 46. 



Jaw with 6-10 strong ribs. Radula having outer side cusps 

 developed on middle and lateral teeth. Marginals with bifid inner 

 and simple outer cusps. Genital system (pi. 62, figs. 22, 23, H. 

 arbustorum} showing the features usual in Helicigona throughout. 

 The two simple mucus glands are very long; dart sack containing 

 a curved dart (fig. 22) like that of H. lapicida. Diverticulum bound 

 to uterus by a wide membrane traversed by blood vessels. 



Distribution, middle and north Europe, upper Pliocene and Loess 

 deposits. In the modern fauna this species or group of species, is 

 distributed from the northern boundary of the Olive zone (Pyre- 

 nees and Alps) to Sweden, enjoying a far greater range than any 

 -other member of the genus Helicigona, especially in its ability to 

 withstand the cold. The number of local races is remarkable, and 

 ptheir study is much complicated by the fact that forms with a simi- 

 lar aspect occur in widely separated localities, probably due to par- 

 allel development. Typically many of these varieties are very 

 different, but intermediate forms seem to abolish most boundary 

 Klines ; so that Kobelt, in his latest contribution on the subject, is not 

 willing to endorse even the main forms as species (Iconogr. n; F., 

 vi, p. 60). 



The spelling of this name given above is that of Leach, Beck 

 and other early authors. Von Martens has changed the name to 

 " Arionta" on etymological grounds. The single well defined spe- 

 cies H. arbustorum, is a typical Helicigona in anatomy, having the 

 diverticulum bound to the uterus by a broad membrane, the two 

 long, cylindrical mucus glands inserted on vagina, and other feat- 

 ures diagnostic o that genus. The American species referred to 

 Arionta by authors present nothing of the sort ; the diverticulum has 

 #0 membrane ; the mucus glands are bulbiferous and inserted on 

 xiart sack, etc., etc. 



H. arbustorum L., iv, 117. v. picea Zgl., iv, 117. 



v. conoidea West., iv, 118. wittmanni Zow. 



vv. calcarea Hogb., iv, 118. v. jetschini Ulic., iv, 117. 



