42 



FKMJTHJOF ØKLA.ND. 



M.-X. Kl. 



.s])tcimens. Ilicy are situated close to the edge of the shield, at the highest 

 sejjarated from the maigin l)y a narrow pale stripe, while in the other 

 species they form a curve over the respiratory orifice (fig. i ). 



The jaw (fig. 35—36) is about one mill, broad, semilunar, but with 

 varying outlines; the middle part of the concavity is often slightly convex. 

 As a rule the colour is pale amber, in old specimens not rarely with a 

 taint brownish tinge at the lower edge. 



The number of ribs is about 6 — 12, but as some of them may be 

 indistinct, it may be difficult to determine the exact number. The jaw 

 is scarcely distinguishable with an\- certainty from that of Arioji cir- 

 ciiiuscripfits. 



T il c radula (fig. 37 — 39) has a Irngth of about 3 mill., but presents 

 too great a lii<:cness to that of Ar ion sn/jfnsciis and Arioii ci/r/tniscripins to 



Fig. 37- Fig. 38. 



Radular teeth of Arum hortensis, ^'^A. Radular teeth of Ar ion hortensis, ^^i\. 



(abnormal). 



admit always of an undoubted identification of the species. With relative 

 ease it may be distinguished from the first, the mesocone of its median 

 tooth having distinct secondary cusps, and further by observing that the 

 inner marginal teeth very often have no ectocone. When present, the latter 



character in most cases indicates a difference 

 from Arioii circiDuscriptus, but, to judge from 

 the figure in Taylor's Monograph, this species, 

 too, may sometimes have a single cusp in the 

 inner marginal teeth. 



As will be seen from the figures, the 

 teeth show small variations in their shape, e. g. 

 in the length of the distance from the anterior 

 edge of the basal plate to the outer base of the 

 ectocone. — Abnormities, also, are found (fig. 39). 

 Reproductive organs (fig. 40 — 41). In spite of a certain degree 

 of variation, these are most characteristic, at anv rate in the Norwegian 

 stocks, . the specific characters, as usual, being found in the lower parts of 

 the organs. The ovispcrtnatodiict {o-sp.-d.) divides into two tubes of about 

 equal length: one is the oviduct [o.), which in its upper half is slender, 

 but then dilates conically, the other the slender vas deferens \v. d.\ and 

 the cpipliaUus \cp.\\ the latter, too, dilates downwards and has a bulbous 



Fig. 39. Radular teeth of 

 Arion hortensis, with ab- 

 normity, 400,1. 



