34 



I- Kil) I II KU- ØKI.A.NO. 



M.-X. Kl. 



Arion subftiscns and Arion liortnisis. i lowcvcr, it often differs from 

 the former, in as iiiucli as the central teeth have a slender mesocone with 

 distinct secondary cusps, and from the second by the fact that the marginal 

 teeth usually have two cusps. Otherwise the shape of the teeth varies 

 (compare fig. 24 with 25), and, judging from the figure in Taylor's Monograph, 

 the ectoconus of the inner marginal teeth may disappear, the species thus 

 overlapping the range of variation of Arioti liortoisis. 



Reproductive organs. As a rule these are very characteristic, 

 but my examinations have proved them to be highly variable in several 

 respects (fig. 26 — 33 1. 



0.-5 p. -d. 



relr. 



Fig. 26 — 27. Lower parts of the reproductive organs of Arion circuniscriplus, ';'l . 



(itr. atrium genitale, ep. epiphallus, o. oviduct, o.-sp.-d. ovispermatoduct, rcc. receptaculum, 

 retr. retractor, v. d. vas deferens. 



The ovispermatoduct (o.-sp.-d.) divides on one side into the oviduct (o.), 

 which is shorter and more slender than in the allied species, having also 

 an almost equal breadth, on the other side into the vas deferens [v. d.). The 

 latter proceeds into the epiphallus [ep.], which dilates gradually and not 

 seldom has a distal bulbous enlargement. Sometimes the epiphallus shows 

 dark spots of pigmentation. 



The stalk of the receptacuhtui [rcc.) is often dilated at its base; the 

 bladder with rare exceptions is pointed, a character which is never found 

 distinctly developed in other species (though it may be slightl}' indicated 

 in Arion suhfuscus, fig. 21). However, this point of the receptaculum 

 varies greatly, presenting all transitional forms from a marked appendix 

 (fig. 29, 30) through less marked (fig. 27, 31 — 32) to cases where it is 

 quite absent (fig. 28). The range of variation thus overlaps that of Arion 



