146 



HISTORICAL PALEONTOLOGY. 



Fig. 86. a, Spirorbia omphalode natural size 

 and enlarged, Devonian, Europe and America ; 

 b, Spirorbis Arkonensit, of the natural size and 

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

 the reverse direction. Devonian, America. (Orig- 

 inal.) 



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 

 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 

 yet further diminution 



Fig. 87. a 6, Spirorbis laxus, enlarged, Upper since tne close of the 



Silurian, America ; c, Spirorbis spinulifera, of the Tinner Silurian Tn both 



natural size and enlarged, Devonian, Canada. (Af- ~ PP ^ ?' 1 



ter Hall and the Author. ) America and Europe 



quite a number of gen- 



sric 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, 6), 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 



