NILS HJ. ODHNER, PTISANULA LIMN^OIDES. 15 



is perhaps Diaphana. Neither Newnesia nor Diaphana have 

 parapodia, jaws or stomach plates, and the radula is very 

 narrow, being triseriate in Diaphana, uniseriate in Newnesia» . 

 Further, there are rudimentary tentacles in the anterior 

 corners of the cephalic disc and an external seminal groove. 

 In many of its characters Newnesia approaches Ptisanula too, 

 and the radula of this form seems to be interraediate between 

 Diaphana and Newnesia, owing to its rudimentary or reduced 

 lateral laminse. On the other hand, however, Newnesia has 

 its head-shield prolonged behind into two well-developed, 

 grooved processes, and has a shell resembling that of Aplu- 

 strum. Eliot assumes that it might perhaps constitute a 

 form connecting the Bullacea and the Lophocercidce together. 

 The difference in characters between Diaphana and Pti- 

 sanula on the one hand and the other Scaphandridce on the 

 other justifies keeping them apart and placing the former in 

 a distinct family, Diaphanidce, to embrace probably Newnesia 

 also. Our present knowledge, however, of the affinities among 

 Tectibranchia is still very superficial, and further investiga- 

 tions must be carried out before their delimitation into natural 

 groups can be undertaken with any pretence to scientific 

 accuracy. 



