30 pnocF.r.Dixns oe tiik 



of lletorostraci, reiiresented b}' larpjer species, wliidi are also 

 armoiireil with ])iale.s and scales, but sbow little or no trace of tbe 

 iintl(M'lyinu; soft parts. iJrejmiiaspis (fig. 2), from the Lower 

 Devonian of (^iniinden, Eifel, is tbo best known genus, and several 

 s]ieciiuons liave been found with nearly all the dermal plates in 

 their natural i)osition. It is a luueli dejjivsscd, almost sKatc- 

 sha]ied fish, with a very short rostrum and the orbits piercing a 

 pair of small antero-lat<M-al jilates which iire dii-ected both 

 lat(M-ally anil upwards. As in the I'teraspidians, the greater |)art 



Fig. 2. 



Fig. 3. 



... 



/ 



Fig. 2. — Restoration of Drepcniaxpix (jrtmtoidoiensis, dorsal aspect, from tlie 

 Lower Devoni.in of Giiiliiulen. Eil'el, about oiie-qiiarter iiat. size. 



Fig. 3. — Drawing of nearly complete fossil o!' Phi/llolcpin coiicnUrica. dorsal 

 aspect, from the Upper Old Red Sandstone, Dnra Den, Fifcsliire, about 

 oue-tliird nat. si/e. The lines radiating from the centre of the anterior 

 median dorsal plate probably represent seusorj- canals. British Museum 

 no. P. 11912. 



of the back is covered by two mediati plates, of whicJi the binder 

 is the larger and cleft bfliind for the insertioii of a small spine. 

 Smaller jilates surround these in front as well as at the sides, and 

 the hindmost laterals seem to enclose a pair of branchial openin"-s. 

 Again, as in the Pteraspidians, tlie greater part of the; ventral 

 surface is covered by one large median plate, and in front of this 

 a number of small plates surround the mouth in an uiuletermined 

 nmiiner. The small .scaly tail is laterally compres.sed, and the 

 large fulcral scales on its dorsal border form a close series 



