56 THE NAUTILUS. 



of the genus thus defined have been distributed by New Zealand 

 authors into the following groups which they regard as genera : 

 Geronfla Hutt., Therasia Hutt., Tlinlax-na Alb., Pysra Hutt., 

 Pijrrha Hutt., Plienacohelix Suter, Pididoimx Suter, Amjthidoxa 

 Alb. and Calymna Hutt. These sections or subgenera are founded 

 upon various modifications of the shell or jaw, but they have not 

 sufficient distinctness to rank as genera, unless we understand that 

 term in a much more restricted sense than it has been used by the 

 majority of conchologists or zoologists generally. These minor 

 divisions are however natural groups and they are useful if we do 

 not overestimate their importance. The sections or subgenera of 

 this genus may stand as follows, the sequence of names being 

 chi'onological.^ 



Geroutla Hutt, 1883 (Type G. jjantheriita Hutton.) 



Therasia Hutt., 1884, (Type C. eelinde Gray.) 



Calymna Hutt., 1884, -f Amphidoxa Hutt. not Alb. (Type C. 

 costulata Hutt. 



PyrrJm Hutt., 1884, (Type P. cressida Hutt.) 



Phenacohelix Suter, 1891 (Type H. j)ihda Rve.) 



Allodiseus Pils,, 1892 (Type H. dimorpha Ffr.).^Pysra Hutt., 

 1884, non Stal, 1876. 



Suter ia Pils. 1892 (Type H. Ide GmY).=Patulopsis Suter, 1891, 

 non Strebel, 1879. 



TJialassohelix Tils. 1892 (Type -if. zelandice Grsiy).= Thalassia 

 Hutton (? and of Albers,) not Thalassla Chevrolat, 1834. (Coleopt.) 



It will be noticed that Amphidoxa has been dropped or rather 

 united to Calymna. The true Amphidoxa has not been found else- 

 where than upon the island Juan Fernandez and the neighboring 

 South American Coast. I have compared specimens with the New 

 Zealand shells and find that there is not the slightest ground for 

 supposing them congeneric. I am disposed to believe that the New 

 Zealand Thalassias do not belong to the same genus as the Austra- 

 lian subriigata Pfr., the tyjie of Tlialassia Albers. The other 

 departures from the ustige of New Zealand authors are sufficiently 

 explained in the above list. 



^ The genus Phacussa of Hutton is included by Suter. It may prove tliatthe 

 Zonitoid aspect of the dentition of that form is a secondary modification and not 

 truly Zonitoid. In this case the group will be included among the present forms; 

 otherwise it must remain in Zonilida?, where Hutton placed it. 



