26 



KKIiyrHJOF ØKI-AND. 



M.-N. Kl. 



AnUrinily ihc i;iw |)rcs(;nt.s ah^ut lo 12 ritjs, but the number is 

 inconsiaiit. liroad, flat and close-set when typical, the ribs are liable to 

 variation, wliiih, to jiidge from the figure in Taylor's work, may even go so 

 far as to make identification difficult. In the Nor-wegian 

 forms, however, the determination is often easy owing 

 Id the Ijioad ribs with narrow interspaces. — Not 

 rarely the riljs on one side are unlike that of the other. 

 The rad 11 la (fig. 16 — 18| attains the length 

 of 5 mill., and can be identified by observing that 

 the mesocone of the median tooth is constricted at 

 the base, whilst the distance from there to the point 

 of the mesocone is equal to or a little shf)rter than the distance to the 

 anterior edge of the basal plate. (It should be remembered that in the 



Fig. 15. jaw of juve- 

 nile An'oii siibfiiscHs, 22/1 



Fig. 16. Radular teeth of 

 ArioH sub fusens, 400; ]_ 



Fig. 17. Radular teeth of 

 Ariou snbfiiscits, ■*00 1 . 



figures the teeth as usual are placed with the anterior edge downwards). 

 The mesocone of the median tooth has no distinct secondary cusps. 



Otherwise the radula presents the same variations as in Arion atcr; 

 abnormities, too, are frequent. 



Organs of reproduction (fig. 19 — 21). 



The ovispcrmatodiict [o.-sp.-d.) divides into a slender vas deferens {v. d.) 

 which further proceeds into the long, gradually dilating epiphalli(S \ep.), 

 and into the oviduct [o.]. The latter is quite characteristic, dilating 

 downwards either gradually or suddenly at the point of insertion ot the 

 genital retractor. It may, however, be remarked 

 that the oviduct forms almost a right angle with this 

 point as apex, and when stretched out, at this place 

 there is often formed a fold which may be mistaken 

 for sudden dilation. . The two branches of the genital 

 retractor (retr.) are of about the same size, one in- 

 serating to the upper half of the oviduct, the other 

 proceeding on to the stalk of the receptaciiluui \rcc.\. 

 This generally has a regular oval bladder, which in 

 rare cases, however, ma}' exhibit indications of a 

 pointed end (fig. 21), thus forming a connecting link 

 wùth the peculiar receptaculum of Ariou circuniscriptus. 



X5 





 (abTiornia,X) 



Fig. 18. Radular teeth of 



Ariou siib/iiscus, with 



asymmetrical central tooth, 



400/, . 



