EXPLANATION OF THE PLATES. 
Fig. 2.—a, 6, c. OLDHAMIA RADIATA, Forbes. 
. Portion of rock, the surface of lamine being altered in colour by che- 
mical action, upon which are grouped well-defined stellate examples of 
O. radiata, showing the radiation of each from a common centre, their 
division and subdivision into branches and branchlets, some of them 
assuming a plumous appearance. ‘The rock, a closely laminated, fine 
grained, greenish grit, shows every layer to be more or less covered by 
these remarkable fossils. From the rocks exposed at low water, called 
‘¢ Periwinkle Rocks,” Bray Point. 
. An example of O. radiata, selected from amongst others as showing a 
more dense, plumous, and irregular branching appearance ; also, very 
conspicuously, the jointed or intermittent character of the several 
branches, some of which are extended into a single thread-like filament, 
an inch or more in length; in purple laminated fine-grained grits, from 
To on shore at Bray Head; collected. by the Geological Survey of 
reland. 
. An isolated star, doubtfully referred to this species, in which the branches 
are very few, and much lengthened out ; collected by the Geological Sur- 
vey of Ireland from the same beds with O. antiqua (fig. 1, f) at Kilrud- 
dery Demesne, near Bray Head. 
