NORWEGIAN OPISTHOBRANCHIATE MOLLUSCA 



given by Grieg, and those of T. plebeia published by Bergh (1884, 

 Malac. Untersuch. H. XV), G. O. Särs (1878, radula, Tab. XV, 

 fig. 1) and Alder & Hancock (Monograph, Tritonia), 1 am now 

 convinced that the form represents a distinct species, and is not 

 to be referred to T. plebeia. From the latter it differs in the 

 following respects, viz.: 



Its size is larger, that of T. plebeia generally attaining about 

 17 mm only (Bergh) but occasionally more (30 mm is given on 



Fig. 1. Radula of T. griegi (cf. p. 46). 



I he plate in Alder & Hancock). The main colour of T. griegi 

 is white or yellowish, whereas in T. plebeia dark markings (of 

 gray, black, or brown) are prevalent. Further in T. griegi the 

 genital opening is situated beneath the distance between the 

 3th and 4th, the anus between the 4th and 5th gill tuft; in 

 T. plebeia the respective positions are between the 1st and 2nd, 

 and between the 3rd and 4th branchial papilla. 



On the frontal veil there are normally 12 papillae, this is 

 the case m the present specinHen; one of the original specimens 

 was aberrant in this point, possessing 11 (cf. Grieg). In T. 

 plebeia there are 8, at the utmost. 



the structure of the radula the present form exhibits 

 some differences of importance. Not only is the number of teeth 

 by far greater than in T. plebeia, but the shape of them is 



