66 Dr. J. EF. Marr—The Ashyillian Series. 
The trilobites have up to the present received most attention. 
By means of these Crustaceans we can most readily separate the Ash- 
gillian Beds from those of Caradocian and Valentian ages. 
The occurrence of Staurocephalus in the lower part of the Ashgillian 
Series and of Dalmannites mucronatus in the upper part (and also in the 
lower) has frequently been noted. A few remarks upon each of these 
forms will be useful. 
The term Staurocephalus Beds was first applied to rocks belonging 
to the Ashgillian age in Sweden and subsequently in Britain. “The 
Swedish form is “Staurocephalus clavifrons, Ang.  Staurocephalus 
globiceps, Portl., is probably identical with the Swedish form. Lastly, 
Salter (Mon. Pal. Tril., pl. vi) figures a form from Rhiwlas as 
Staurocephalus Murchisoni, Barr. It may be noted that Barrande’s 
type form is from beds of Ludlow age. It is doubtful whether even 
the British Wenlock forms which are referred to this species are 
correctly assigned, and there are grave doubts as to the identity of the 
Bohemian and Rhiwlas forms. The Ashgillian Stawrocephali require 
careful study, and the three forms above noted will probably prove to 
be identical or closely allied, and separable from the Wenlock and 
Ludlow fossils. 
The genus, if found in Caradoc rocks, is extremely rare therein. 
It is also far from common in rocks of Valentian age, and its wide 
distribution in the Ashgillian Beds is distinctly noteworthy. 
Dalmannites mucronatus, Ang., is particularly abundant in beds of 
Ashgillian age, and is very useful when separating them from the 
Caradocian deposits, in which, so far as I am aware, it has not been 
found. On the other hand, it passes up into the Valentian rocks, both 
in Britain and in Scandinavia, and forms one of the few connecting 
links of the Ordovician and Silurian faunas. 
This form requires study. Angelin describes two species, namely, 
Dalmannites mucronatus, which in Sweden is a Valentian form, and 
D. ewcentra, which occurs in the equivalents of the Ashgill Shales. 
Salter also separated the North of England form from the type 
mucronatus as var. appendiculatus. Later writers have referred all to 
mucronatus, and if the Ashgillian and Valentian forms be distinct they 
are certainly closely allied. 
While speaking of the Phacopes, we may note that the group 
Chasmops, so abundant in rocks of Caradocian age, appears to be 
absent from the Ashgillian Beds, and that the group Phacops proper, 
which is found abundantly in the overlying Valentian rocks, has also 
never been recorded from beds of Ashgillian age. 
Turning now to the genus Trinucleus, we find that this form, so 
abundant in all Ordovician rocks, is well represented in the highest 
Ashgillian Series. The sudden disappearance of this form at the top 
of the Ashgillian Beds is one of the most important means of 
separating these from the Lower Valentian (Llandovery) Beds. It 
is true that Zrinucleus has been more than once recorded in beds of 
Llandovery age, but even if these records be correct the genus is 
extremely rare in them. Let us for a moment notice these records 
In Cat. Camb. and Sil. Foss., p. 78, Salter records 7. conceniricus 
from the Lower Llandovery of Pen-y-craig. I find the actual 
