104 SECTIONAL ADDRESSES. 
graptolite zone of Dicranog. clingani, but others also occur showing 
that the line has begun to branch in various directions leading into 
different species-groups, the details of which have still to be worked 
out. It is, however, clear, I think, that the state of evolution of the 
glabella lobes may afford a valuable index of the age of the beds in 
which it occurs. 
Further investigation is required to show how far this parallel 
evolution takes place at approximately the same time in remote areas 
in different species-groups. So far as I have investigated the problem 
it would appear to be broadly true in the case of the deeper-water 
paces acs nasa yet ot Daal 
: 
_———— we oo 
——_—_ em = 
-= 
— ew eS em ew — 
_ 
ae eer 
—=— eee oe 
SS 
mee 
| 
a 
——-~—- ee 
— ow we i 
eR ae 
-—— — eS oe 
=} 
1. Calymene tristani. 3. Calymene parvifrons mut. 
(Zone of D. extensus.) (Zone of D. bifidus.) 
2. Calymene parvifrons. 4. Calymene cambrensis. 
(Zone of D. hirundo.) (Zone of D. Murchisoni.) 
5. Calymene planimarginata. 
(Zone of Dicranog. clingani.) 
faunas, for so far as the graptolites are concerned the outstanding stages 
in evolution are reached in the majority of cases at approximately the 
same time along many different routes, though there are some excep- 
tions, for which the reason is, however, usually obvious. So far as 
the Calymenes are concerned it is of great interest to note that those 
of Bohemia, though constituting a different species-group from those 
found in this country, undergo a precisely similar evolution at the 
same time; thus C. arago of D.1. y shows a. very slight and faint indi- 
cation of a third lobe with a straight outer edge to the glabella, a pre- 
cisely similar stage to that of C. parvifrons in this country; so, too, 
