254 Mr. C. Lapworth on the Geological 
general palaeontologist of the time in the Graptolite as a 
geological index, yet compare by no means unfavourably 
with the preliminary efforts of systematists in other groups of 
fossils during the initiatory and obscure stages of their 
investigation. 
The more noticeable efforts in this direction were the sum¬ 
maries in the works of Barrande, Salter, and Hall, and in the 
various memoirs published by Professor Nicholson. 
In his classical work on the Graptolites of Bohemia, pub¬ 
lished in 1850, Barrande gave an exhaustive summary of the 
facts at that time recognized with respect to the geological 
range of the Rhabdophora Misled by Professor Phillips’s 
erroneous enumeration of Didymograptus Murchisoni (Beck) 
among the fossils afforded by the black (9/enws-bearing shales 
of the Malvern Hills, and by Sedgwick’s distinct assertion 
that the Graptolite-bearing Skiddaw slates were of the age of 
the Lower Cambrian, Barrande reluctantly looked upon the 
Graptolites as making their first appearance in, or imme¬ 
diately below, his Primordial zone. The upper limit of their 
vertical range he placed in the Ludlow formation. The epoch 
of their maximum development corresponded, he believed, to 
the middle of the Lower Palaeozoic age ; in other words, they 
reached their maximum at or near the period when the lowest 
beds of Murchison’s original Upper Silurian formations were 
laid down. He recognized most distinctly the restricted 
range of the genera Hastrites and Gladiolites , and hinted that, 
in all probability, they would be found to be exclusively con¬ 
fined fo the rocks of the third fauna. From the fact that the 
Rhabdophora attained their maximum development in the 
Llandeilo-Bala beds of the United States, Britain, and Scan¬ 
dinavia, while they do not become abundant in Bohemia till 
we reach the horizon of the Llandovery, he believed that the 
anteriority of the existence of the Rhabdophora in the former 
countries might even then be regarded as established, not 
only for the group as a whole, but also for many of its subor¬ 
dinate forms. This conclusion, which implied the presence 
of a fauna of a typical Silurian character in the higher strata 
of the Ordovician of America and North-western Europe at a 
time when the typical Ordovician fauna remained unchanged 
in the Bohemian basin, he fortified by coincident proof from 
the behaviour of the genera of the Crustacea and Brachio- 
poda ; and it has often been employed by him subsequently 
with great effect in defence of his remarkable theories of 
migration and colonies. 
* Grapt. de Boheme, pp. 20-32. 
