14 ARKIV FÖR ZOOLOGI. BAND 8. NIO 25. 



named is a more primitive genus than the last, as regards its 

 genital apparatus for instance, and also the nervous system, 

 the absence of tentacles and the form of the shell ; it is somewhat 

 more advanced, on the other hand, thanks to an elementary 

 armature of the stomach and its more specialized radula, in 

 which the lateral teeth are highly reduced. As respects the shell, 

 Ptisanula is without resemblance outside the most primitive 

 Tectibranchia, the Actceonidce. Some forms of Diaphana and 

 Retusa may have a somewhat produced spire, it is true, but 

 this only projects slightly above the body-whorl. The shells 

 of Actceonidce have usually a denticulate columella and a punc- 

 tured or spiral sculpture ; there are some forms, however, 

 which exhibit aberrant characters, approaching those of Pti- 

 sanula, some forms of Leucotina, which are, however, always 

 sculptured, and of the fossil genus Actceonina, which is, how- 

 ever, imperforate. In 1883 Watson described a recent shell 

 belonging to the last-named genus, A. chariis, dredged by 

 the »Challenger» at the Azores, in 1000 fathoms. It shows 

 conformity to Ptisanula, but it is imperforate, only rimate, 

 spirally sculptured and with no columellar convexness. The 

 soft parts of the forms mentioned of Actceonidce are still un- 

 known, and so nothing can be said about the possibly existing 

 affinities between them and Ptisanula. The latter consequently 

 has every right to be considered established as a distinct 

 genus. 



Among the members of the prosobranchiate genus Odo- 

 stomia, containing small forms, ther are some shells with a 

 striking resemblance to Ptisanula, e. g. O. Normani Friele 

 1878, but in it the whorls are 4 Va by 2 mm in length 

 and the spire is considerably higher and the convexity of 

 the columella is located as its upper extremity. A closer 

 conformity is exhibited by a small shell from Alaska. O. 

 (Evalea) nunivakensis, described and figured by Dall and 

 Bartsch in 1909. »It has five post-nuclear whorls and mea- 

 sures: Length 3 mm., diameter 1,6 mm.» But the »entire 

 surface is crossed by fine lines of growth and exceedingly 

 fine, closely spaced, wavy spiral striations» (P. 194). 



In 1906 Eliot described the anatomy of an antarctic 

 Tectibranch, that was established by E. A. Smith in 1902 

 as a new genus and species, to which he gave the name 

 Newnesia antarctica. Eliot considers, that »its nearest ally 



