NORWEGIAN OPISTHOBRANCHIATE MOLLUSCA 21 



Goniaeolis possesses on the other hand some, features in 

 its organization which mediate to the Cladohepatic Nudibranchia, 

 and to Aeolidoidea especially. The shape of the radula, the pre- 

 sence of papillae on the notum, and of oral tentacles are all 

 characters common to this group. It seems to be not improbable 

 that the latter is derived from forms similar to Goniaeolis. In 

 some of the Aeolids we still perhaps trace indications of this 

 origin. In Chlmnylla typica of Bergh {Goniaeolis typica Bergh, 

 not M. Sars) the genital apparatus is very simple, and rather 

 hke that of Goniaeolis, though it has a spermatocyst as distingui- 

 shing mark (cf. Bergh 1886, pl. III, fig. 25). In the same species 

 the head is expanded at the sides {1. c, fig. 1); these side lobes, 

 as well as those of Coryphella salmonacea (see further below) 

 may perhaps be the homologa of the cheek lobes of Goniaeolis. 

 The radula in the three forms is similarly triseriate. 



The opinion expressed here as to the origin of Aeolidioidea 

 via Goniaeolis from Pleurohranchaea-shapeå Opisthobranchia 

 is in opposition to the view maintained by Pelseneer (1894) that 

 Tritonia is the ancestor of all Nudibranchia. On the other hand 

 the same opinion is in agreement with the supposition expressed 

 by GuiART (1899)1 who finds that the nervous system supports 

 a derivation of the Nudibranchia from Pleur obranchidae. We 

 have remarked (under the heading of fam. Tritoniidae) that Tri- 

 tonia must be considered as representing its own separate line 

 of development, and for this reason cannot be the immediate 

 origin of the Aeolidoidea. There are, consequently, some important 

 facts v^hich speak against Pelseneer's idea of the affinities and 

 which make it likely that these must be otherwise established. 

 Some further remarks on this matter will be given later on. 



1 Contribution à la phylogénie des Gastérop. et en part, des Opistliobr. 

 etc. Bull. Soc. Zool France, 24. 



