142 
THE LOWER GALLERY. 
In the drawers below the Flat Cases will be found, among 
other specimens, a collection of fossils from the Durness lime- 
stone, in Sutherlandshire, including chambered shells of cepha- 
lopods, like Orthoceratites. The lower and middle parts of 
this limestone are of Cambrian age, but the higher members may 
be Lower Silurian. 
The Silurian System, named by Murchison from the ancient 
British tribe of the Silures, may be divided into a lower and 
an upper group of beds. The Lower Silurian group includes the 
Arenig, the Llandeilo, and the Bala beds — three divisions named 
respectively from the Arenig Mountains, from. Llandeilo in 
Carmarthenshire, and from Bala in Merionethshire. Lower 
Silurian fossils occupy a large number of Flat Cases. Here will 
be seen the noble trilobite Ogygia Buchii, from the Llandeilo 
flags, and also some large species of Asaphus. The term 
Caradoc beds, used on many of the labels, is borrowed from 
Caer Caradoc, in Shropshire, where shelly sandstones occur 
approximately of the same age as the Bala limestone. Many of 
the Caradoc specimens show numerous casts of the shells of 
brachiopods. 
Of all fossils in these Lower Silurian formations the most 
characteristic are the curiously serrated bodies called Graptoliies 
by Linnaeus, — ( grapho , I write, and lithos, a stone) — from tho 
fanciful resemblance of their rem ains in the stone to quill pens 
with the feathers cut. In Wall Case 4 are some excellent, 
examples of these fossils, especially from the Llandeilo shales ; 
whilst a large diagram above illustrates their structure and 
suggests their relationship with the living sertulariars. Grapto- 
lites occur throughout the Silurian system, and many of them,, 
having a very limited geological range, are useful as characteristic 
fossils of particular zones. 
The fauna of the Upper Silurian rocks — including the Llan- 
dovery, Wenlock and Ludlow groups — is well represented in Wall 
Cases 6 to 10 , and Flat Cases IS to 28. The Wenlock limestone 
of Dudley is marvellously rich, and many fossil-crowded 
slabs are shown in Wall Case 8. The fossils include corals, — 
both simple forms, or those growing singly, like Omphyma, and 
composite forms, or those aggregated in reef -like masses, such 
as Favosites. Cyathophyllum, and the curious “ chain coral ” called 
Halysites . Some thin sections of coral are here mounted as. 
transparent objects. Here, too, are many of the Wenlock crinoids, 
or “ stone lilies/’ each composed of a long -jointed flexible 
column supporting a cup with the rim surrounded by a number 
of long fringed arms. Some large slabs of W T enlock shale are 
notable for their fine examples of Actinocrinus. The Wenlock 
trilobites, in the Flat Cases, are remarkably fine and well 
preserved, and attention may be specially called to the large 
examples of Homalonotus and to the fine specimens of Calymene 
Blumenbachii, known as the “ Dudley locust.” Many of the 
trilobites were capable of rolling themselves up into a ball, like- 
