NORWEGIAN OPISTHOBRANCHIATE MOLLUSCA 35 



General Remarks on the Species of Doto. 



A great number of species of Doto have been described, but 

 the specific vakie of some of these is doubtful. No research has 

 been made to clear up the delimitation of them, a task which 

 seems to meet with many difficulties because the characteristics 

 are distinct in the living state only and hardly discernible in 

 specimens preserved. For the purpose of distinguishing the „spe- 

 cies" the colour comes in the first place, and, in the other, the 

 number and the form of the papillae. From all other species 

 D. crassicornis differs in its thick wrinkled rhinophores sur- 

 rounded by short and wide cylindric vaginae with simple, not 

 expanded nor scalloped margins. In all other species the rhino- 

 phores are thin, staff-like and smooth when extended, and the 

 vaginae have expanded margins. On the coasts of Scandinavia 

 have hitherto been observed, beside the just named form, only 

 D. fragilis and D. coronata. It is, however, possible that one 

 or other of the forms occuring on the British coasts may be 

 found, for instance D. cinerea, D. cuspidata or D. pinnatifida, 

 which should be looked for. The last-named species is most 

 like D. fragilis, but has a series of small tubercles along each 

 side beneath the ^papillae (cf. Alder & Hancock, pi. 45). D. 

 cinerea resembles in the number of papillae D. coronata, but 

 lacks its red colour, especially the characteristic rings on the 

 papillär tubercles; D. cinerea has an ashen gray colour with 

 a dark dorsal stripe and the tips of the papillär tubercles dotted 

 white (cf. Vayssière 1888 ^ pl. 4, fig. 5). D. ciispidata also lacks 

 the red rings on the papillae of D. coronata which have more 

 pointed and produced tubercles; the rhinophores, in addition, are 

 scalloped jn the frontal margin (cf. Eliot, in Alder & Hancock, 

 1910, pi. 5, figs. 1—3). The last-named form may perhaps be 

 only a variety of D. coronata. A trace of lobation can be 



^ Recherches Zool. et. anat. sur les MolJ. Opisthobranches du Golfe de 

 Marseille. IL Ann. Mus. Hist. Nat. Marseille, T. IIL 



