204 



CEP H ALA SPIDOMORPHI 



large fin-like lobe, covered with scales continuous with the shield at its 

 base, projects from each side of the body behind the cephalic shield in 

 Cephalaspis (Fig. 173 [505, 276, 326]). 



Cephalaspis, Ag., and A uchenaspis, Ag. (Tlnjcstcs, Eich.) ; Upper Silurian 

 and Devonian, Europe. Eiikeraspis, Lank., Silurian, and Didymaspis, 

 Lank., Devonian, England. 



Diagrammatic restored outline of AtdeaspU tessellata, Iraq., the tail being turned so as to 

 appear in profile. The orbits are shown near the middle of the head-shield, and in front of 

 them the antorbital fossa and median pore. (After Traqnair.) 



Family Tremataspidak The almost smooth cephalic shield is con- 

 tinuous round the sides on to the ventral surface. Ventrally, behind the 

 mouth, is an area covered by closely fitting plates, and between these and 

 the edge of the shield are a series of apertures, presumably branchial. 

 The interorbital plate is free ; the orbits roofless. No lateral flaps are 

 known [371, 325]. 



Tremataspis, Schmidt; Upper Silurian, Russia (Fig. 176). 



Order 3. ANASPIDA. 



An order founded by Traqnair [4G6] for the reception of two 

 genera of very aberrant structure from the Silurian rocks of Scot- 

 land, Lasanius and Birhenia, to which lias been added a less well- 



Birh nla eUgans, Traq. : restored. (After Traquair.) c.f, caudal tin ; d.f, dorsal fin ; 

 I. p. lateral openings, possibly branchial ; o, orbit; r.s, large ventral scales. 



