78 THE CONSTITUTION OF THE GASTROPOD PROTOCONCH, 



Uymatiam tritoms Linn., (the most dissimilar pair of radulse 

 as yet known in the genus) are much less than the differences 

 between the radulae of Meyalatractua aruunus Linn., and J/. 

 nuixintas Tryon {^vide 31), and that in this case there can ue 

 no doubt that the two species belong to the one genus. Other 

 comparable pairs of species might be quoted to show that 

 radular differences of these small orders are devoid of Phylo- 

 genetic significance. 



Turning next to the operculum, Dr. Dall very correctly 

 suggests that this is possibly of less value taxonomically than 

 adult conchic characters. It is, however, interesting to note 

 that Dall's definition of the operculum in Septa does not 

 apply to that of the type of the genus ( ?), Septa rubicunda 

 Perry, which has the nucleus of the operculum subapical and 

 marginal. In old and large specimens a few perfectly con- 

 centric laminae remove the nucleus from the margin, but even 

 in these it would be quite erroneous to describe it as "sub- 

 central and internal." 



Thirdly, the possession of a distinctive Neamc shell is 

 neither confined to the Septa-gvowp nor present in all its 

 members. The type of the genus ( ?) shows no such stage, 

 neither do ('. pin/iilio Hedley, U. petulans Hedley, nor C. 

 bassi Angas, whilst C. 2}('>'^>'>f-''onianum Perry, has a neanic 

 stage even more marked than that of C tritonis Linn. 



I have dissected Ci/znatiinn spengleri Chemnitz, and C . 

 (Septa) ruhieiuida Perry, side by side, carefully comparing 

 each stage of the dissection, and I fail to find any points of 

 anatomical difference worthy of note beyond the radulas. 



We are thus once more driven back to the adult shell as our 

 final guide in any arrangement of the members of the genus, 

 and here all the evidence points to the complete homogeneity 

 of the group. 



Hedley recently described a new Cymntiuui {petulans), and, 

 adopting Dall's division of the genus, he placed it in Septa 

 "from the general resemblance it bears to »S'. tritonis Linn." 

 (18). In 1903 (17), he described Lotoriuni pumilio; this also 



