412 Mr. F. O. P. Cambridge—A Revision 
diagnosis quotes them as two diameters apart, while the 
rest of the characters coincide with the diagnosis. Can one 
hold that this would exclude the species from being regarded 
as the type? Who is to settle what is the essential cha- 
racter of a genus and what is not? No two authors 
would agree. Personally, I should hold that since we are 
looking for a formal basis, the best one we can find will be 
one of. the species originally referred to the genus, quite 
irrespective of whether the author described their characters 
correctly in his generic diagnosis or not. One would not, of 
course, if the selection of a type were left to one’s self, delibe- 
rately select the species which was thus contradictory to the 
generic diagnosis ; but otherwise one would have to treat the 
species as though there was no contradiction. That at least 
is my personal opinion. The fact is that it is not the generic 
diagnosis (the conception of the genus) which is all-important, 
but the species referred to the name; these are all-important, 
for from one or other of them the characters of the genus 
can always be ascertained, especially if one be selected as the 
type. Dr. Dahl will agree with this, being merely the 
practical application of his Principle IV., though his attitude 
in other respects is not altogether consistent with his adherence 
to the principle he himself claims to have discovered. 
It follows, then, that there are two circumstances under 
which a generic name is clearly valid :— 
(1) When accompanied by a diagnosis and with one or 
more species cited by name or clearly included by reference 
to some former publication. 
(2) When not accompanied by a diagnosis, but with one or 
more species cited by name or included by reference. 
Note.—The generic diagnosis is really included in the 
species. In the case of the Araneidea we should be obliged 
to exclude almost all of C. L. Koch’s generic names if the 
presence of a generic diagnosis were held to be indispensable 
to an available generic name. 
When a Type Species has been wrongly identified. 
Another case giving rise to much difference of opinion runs 
as follows:—An author founds a new genus with a diagnosis, 
and cites as the type a single species already described. It is 
afterwards discovered that the specimen diagnosed is not the 
species the author supposed ; it has been wrongly identified. 
The question is, What now is the type of the new genus, 
the species cited by name or the specimen which has been 
wrongly identified ? 
To. give a concrete case in illustration. ‘The new genus 
