48 



1-)<II>I moi' DK I.AM) 



M.-N. Kl. 



|);irt ol tlic Ifjot liirrow, f|uilc easily flistin^iiishable under a lens; some- 

 times, however, they arc not present. The- tubercles are less extended 

 than in other species, esjxcially on the sides, forming almost regular hexa- 

 gons. Katlier useful for the purjjose of determination I have found to be 

 the single row of yellowish white tubercles directly over the foot-fringe 

 and parallel to the latter; this may also be present in the young of ^r/o« 

 (iter, l)ut in that case with several similar rows on the upper side. 



Lastly there are the often indistinct shield-bands (fig. i), the right 

 one enlarging and enclosing the respiratory orifice, a character that at any 

 rate in Norwegian specimens is most constant and facilitates determination. 



The jaw (fig. 42 — 43) varies very much. It is about one mill, broad, 

 semilunar, with sometimes convex median part of the concave cutting edge, 



Fig. 42. 

 Jaw of Avion mtermcdhts, ^'^h. 



Fig. 43- 

 Jaw of Ar ion iiitcnricdiits, ■^•* 1 . 



20 1 1 



Fig. 44. Fig. 45. 



Radular teeth of Anon intermedins, ^00 1 Radular teeth of Ar ion intermedins, ^O^, I. 



of a yellowish brown colour, often darker in the lower part. The ribs 

 are present to the number of 5 — 10, varying considerably in breadth. The 

 Norwegian stock has a jaw of the common generic type, it being impossible 

 to distinguish it from that of the two preceding species. Very remarkable, 

 therefore, is the fact that foreign stocks present a quite different type of 

 jaw (Taylor 1907, Steenberg 191 i), the whole extent of the anterior 

 surface being occupied by exceedingly broad, close set ribs ; as appears 

 from the figure in Taylor's Monograph, their breadth is at least equal to 

 their vertical extent. 



The radula (fig. 44 — 45) measures 2 — 3 mill, hi spite of a con- 

 siderable variation it seems that an identification of the species is always 

 possible in Norwegian specimens, owing to the shape of the median tooth ; 

 the mesocone is here highly constricted at the base and as a rule is longer 

 than the distance from its base to the anterior edge of the basal plate. 

 Added to this, the length of the lateral cusp is equal to, or generally a 



