Correspondence—Mr. A. J. Jukes-Browne. 237 
should differ from one another in characters of equivalent value, and 
(2) that it is not necessarily wrong “to include in the same genus 
species descended for a long time through entirely different lines of 
ancestors.” There is in fact very little wrong or right in the matter, 
it is one of convenience and of sensible proportional treatment. 
We may admit that the whole family Ammonitide requires 
revision and reconstruction, and possibly that it is desirable to create 
a certain number of new genera out of the old genus Ammonites, 
but I join Mr. Haddow in protesting against the infinite subdivision 
which some paleontologists are trying to force upon us. The old 
principles of classification may not be defensible, but is it so very 
certain that some of the principles now adopted in their stead, such 
as the form of the mouth, are any better? Is there not some analogy 
between the case of the genus Ammonites and that of the genus Heli, 
in which an infinity of peculiar variations occur in the shells without 
any important differences occurring in the structure of the animals ? 
If mere sections and subgeneric groups are raised to the rank of 
genera, the old genera become tribes and subtribes, and Mr. Buck- 
man even wants us to accept names for generic and subgeneric 
groups, ranking between genera and subtribes. Surely, Sir, such 
an arrangement as he gives us in his Monograph on Inferior Oolite 
Ammonites is the height of cumbrousness, and shows the absurdity 
to which the system is capable of being carried. Stated in full this 
arrangement is as follows :— 
Family—Ammonitidee. 
Subfamily—Ammonites (note the termination). 
Tribe—Agoceratidee. 
Subtribe—Harpoceratine. 
Generic group—Hammatoceratidee. 
Generic subgroup—Hildoceratinee. 
Genus— Ludwigia. 
Species—Murchisone. 
Really I think a trinomial or even a quadrinomial system is better 
than this, which is practically a septinomial one. The small section 
of a group which is here elevated into a genus hardly merits a name 
at all, it is a mere section of Harpoceras which may be regarded as 
a subgenus of Ammonites. I therefore take up Mr. Buckman’s 
challenge, and would speak of the species trinomially thus— 
Ammonites (Harpoceras) Murchisone, 
# FA Bs var. obtusa. 
By this method it would still be possible for the stratigraphical 
geologist to speak of it as Ammonites Murchisone, while the paleon- 
tologist who makes a special study of the genus would doubtless 
usually call it Harpoceras; but no other Ammonite could receive 
the same specific name, whereas, if Harpoceras be admitted as a 
generic name, new species referable to that genus might receive the 
same names as those now applied to other well-known species of 
Ammonites; thus we might have Harpoceras cordatus, H. cristatus, 
ete. 
As regards the rectification of erroneous identifications, we are of 
