of the Genera of the Aranez. 411 
A Generic ‘‘ Nomen nudum.” 
Much diversity of opinion appears to exist also on this 
subject, but, none the less, if we are to make any attempt to 
settle the type species of a genus we shall have to make up 
our minds under what circumstances a generic name is valid 
and when a nomen nudum. 
There are two sets of circumstances under which a generic 
name might conceivably be regarded as null and void, and 
one in which it is not easy to decide :— 
(1) When a generic name is proposed and _ published 
without either generic diagnosis or any species cited by name 
or cited by reference to some group name or sectional name, 
involving certain species under them, previously published. 
In this case, since there are no means whatever of ascer- 
taining the characters on which the genus is founded, the 
generic name is null and void. 
(2) When a generic name is published with a generic 
diagnosis, but without any species being cited either by name 
or by reference. 
In this case, again, the type species cannot be fixed, and 
though the generic characters are given, unless a definite 
species be cited or referred to, it is difficult to understand how 
the genus can be valid, seeing that theoretically a genus 
represents a group of species, and must, for practical pur- 
poses at any rate, be represented by at least one species 
definitely cited or referred to. Dr. Dahl would, if further 
proceedings interest him in any way, agree to this, for in his 
analysis of the spirit of the Rules of Nomenclature, in his 
search for the principles on which they are based, he has 
discovered —PRINCIPLE LY. “‘ Typical species, in the rules of 
nomenclature, take the place of the conception of genus”: with 
this result, that “the purely formal basis ts retained, and the 
fluctuating conception of genus avoided.” Quite so! That 
is precisely what we are striving to point out. Our efforts 
are directed to secure this “formal basis,” so as to avoid that 
« fluctuating conception of a genus” which is so exasperating 
to the modern student of the Aranee. 
(3) The next case is a doubtful one. When the species 
quoted or referred to actually contradict the generic diagnosis 
in one or more characters. 
This is a difficult question, because at first sight it seems 
that if a species in any of its characters contradicts the 
diagnosis it cannot be the type of that genus. But sup- 
posing the character is not essential—e. g. the central anterior 
eyes are two and a half diameters apart, whereas the generic 
