1922. No. 5. 



ARIONIDAE OF NORWAY. 



43 



enlargement where it joins the atrium, being less voluminous, however, 

 than the lower half of the oviduct. 



The rcceptaciiliiin [nx.) in Norwegian specimens as a rule has a fragile 

 bladder with irregular outlines, attached to a short stalk. The genital 

 retractor [rctr.] is of different development, presenting all transitions from 

 quite separate branches for the oviduct and for the receptaculum (fig. 40), 

 to a perfect fusion in the first part of the components (fig. 41). The shape 



rSf^ri^. 



Fig. 40 — 41. Lower parts of reproductive organs of Arioii /loitciists, '1. 



at?-, atrium genitale, ej>. epiphallus, o. oviduct, o.-sp.-d. ovi.spermatoduct, rcc. receptaculum, 



rctr. retractor, v. d. vas deferens. 



of the atrium {atr.) varies too, sometimes divided by a transverse con- 

 constriction (fig. 40), sometimes undivided (fig. 41), with intermediate forms 

 between these extremes. Powerful retractors Inserate at the upper part of 

 the atrium. 



The spermatophorc is said to be short and stout, with no denticles. 



Variation. With regard to the inner characters, the variation has 

 been mentioned under the description of the jaw, the radula and the 

 reproductive organs. On account of the differing colour several varieties 

 have been created. In Norway, however, only a single one occurs. But 

 even in this the intensity of the colour of the back, the sides and the foot- 

 sole may somewhat diiïer between one specimen and another; the lateral 

 bands, for example, may be proportionally narrow or extend more or less 



