THE UPPER SILURIAN PERIOD. [25 
plates of these creatures, and some of them (such as the Wen- 
lock Limestone of Dudley) have yielded perhaps the most 
NY 7/7 
ZN 
Fig. 60.—Upper Silurian Star-fishes. 1, Palasterina primeva, Lower Ludlow ; 2, 
Paleaster Ruthveni, Lower Ludlow; 3, Paleocoma Colvini, Lower Ludlow. (After 
Salter.) 
exquisitely-preserved examples of this group with which we 
are as yet acquainted. However varied in their forms, these 
_ Fig. 61.—A, Protaster Sedgwickii, showing the disc and_bases of the arms ; B, Por- 
tion of an arm, greatly enlarged. Lower Ludlow. (After Salter.) 
beautiful organisms consist of a globular, ovate, or pear-shaped 
body (the ‘calyx”), supported upon a longer or shorter 
jointed stem (or “ column”). The body is covered externally 
with an armour of closely-fitting calcareous plates (fig. 62), and 
its upper surface is protected by similar but smaller plates 
more loosely connected by a leathery integument. From the 
upper surface of the body, round its margin, springs a series 
of longer or shorter flexible processes, composed of innu- 
merable calcareous joints or pieces, movably united with one 
