144 



HISTORICAL PALAEONTOLOGY. 



and enlarged, Devonia 

 ircrbis Arkonetisis 



in many specific forms (figs. 86 and 87) ; but almost all the 

 known examples are of small size, and are liable to escape a 



cursory examination. 



The Crustaceans of 

 the Devonian are prin- 

 cipally Eurypterids and 

 Trilobites. Someofthe 

 former attain gigantic 

 dimensions, and the 

 quarrymen in the Scotch 

 Old Red give them the 

 name of " seraphim," 

 from their singular 

 scale - like ornamenta- 

 tion. The Trilobites, 

 though still sufficiently 

 abundant in some local- 

 ities, have undergone a 

 c yet further diminution 



since the close of the 

 Upper Silurian. In both 

 America and Europe 

 quite a number of gen- 

 eric types have survived from the Silurian, but few or no new 

 ones make their appearance during this period in either the Old 



iphalodes, 



Europe and America ; 



6, Spircrbis Arkonetisis, of the natural size and 

 enlarged ; c, The same, with the tube twisted in 

 the reverse direction. Devonian, America. (Ori- 

 ginal.) 



Fig. 88. a b, Spirorbis la: 

 Silurian, Ame ' 



, enlarged, Upper 

 'era, of the 



Spirorbis spinulij, 



natural size and enlarged, Devonian, Canada, 

 ter Hall and the Author.) 



(Af- 



8. Devonian Trilobites a, PJutcops latifrons, Devonian of Britain, the Conti- 

 of Europe, and South America ; b, Homalonotiis armatus, Europe ; c, Pfiacops 

 (Trhnerocephalns) la>vis, Europe ; d, Head-shield of Pkacops (Portloctria) granulatus, 

 Europe. (After Salter and Burmeister.) 



World or the New. The species, however, are distinct ; and the 



