146 



HISTORICAL PALEONTOLOGY. 



the fronds of the commoner Sea-weeds (especially Fucus ser- 

 ratus). These tubes are inhabited by a small Annelide, and 

 structures of a similar character occur not uncommonly from 

 the Upper Silurian upwards. In the Devonian rocks, Spir- 

 orbis is an extremely common fossil, growing in hundreds 

 attached to the outer surface of corals and shells, and appearing 

 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. Some of the 

 former attain gigantic 

 dimensions, and the 



Fig. 86. a, Spirorbis omphalodes natural size 

 and enlarged, Devonian, Europe and America ; 

 b, Spirorbii Arkonensis, of the natural size and 



Fig. 87. a b, Spirorbis laxus, enlarged, Upper 

 Silurian, America ; c, Spirorbis spinulifera, of the 

 natural size and enlarged, Devonian, Canada. (Af- 

 ter Hall and the Author. ) 



quarrymen in the Scotch 

 Old Red give them the 



enlarged ; c, The same, with the tube twisted in name of " seraphim, " 



the reverse direction. Devonian, America. (Orig- . 



inai.) from their singular 



scale - like ornamenta- 

 tion. The Trilobites, 

 though still sufficiently 

 abundant in some local- 

 ities, have undergone a 

 yet further diminution 

 since the close of the 

 Upper Silurian. In both 

 America and Europe 

 quite a number of gen- 



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

 ones make their appearance during this period in either the Old 

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

 principal forms belong to the genera Phacops (fig. 88, a, c, d}, 

 Homalonotus (fig. 88, b), Proetus, and Bronteus. The species 

 figured opposite under the name of Phacops latifrons (fig. 88, a), 

 has an almost world-wide distribution, being found in the 

 Devonian of Britain, Belgium, France, Germany, Russia, Spain, 

 and South America; whilst its place is taken in North Amer- 

 ica by the closely-allied Phacops rana. In addition to the 

 Trilobites, the Devonian deposits have yielded the remains of 

 a number of the minute Ostracoda, such as Entomis (" Cypri- 

 dina"}, Leperditia, &c., which sometimes occur in vast num- 

 bers, as in the so-called " Cypridina Slates " of the German 



