No. 2.] 



WHITEAVES — NEW DEVONIAN FOSSILS. 



95 



Outline of a specimen of the cranial shield of C. Acadicus, 

 shewing the rostral plate (c) in situ. Some of the super- 

 ficial grooves restored from other specimens. Natural size. 



absent, which is almost invariably the case, the anterior margin 

 is concavely emarginate in the centre, the emargination being 

 broad, transverse and bounded on each side by an obtusely angular 

 projection (cZ). On the outer side of each of these projections 

 there is an obliquely and shallowly concave, lateral emargination. 

 In one specimen only (that from which the accompanying draw- 

 ing was made) the rostral plate (c) fits into and completely fills up 

 the central emargination of the front margin of the shield. This 

 plate, which is nearly twice as broad as long, projects beyond the 

 front margin of the shield, its two sides are narrowly rounded 

 but its anterior margin is broken. Test very thin. Sculpture 

 consisting of numerous small, conical tubercles; which are smooth 

 at their summits and marked with fine radiating grooves below. 

 On some of the bony plates of the shield the tubercles are isolated 

 and scattered, but in others they are arranged very distinctly in 

 concentric lines separated by continuous furrows. Besides the 



