284 ARACHNIDA—EURYPTERIDA CHAP. 
The Eurypterid which is best known is Lurypterus fischeri 
(Figs. 161, 162), which is found in the Upper Silurian rocks at 
Rootzikiill in the Island of Oesel (Gulf of Riga). In the 
Fic. 161.—2urypterus fischeri, Eichw. Upper Silurian, Rootzikiill, Oesel. Dorsal 
surface. a, Ocellus; 6, lateral eye ; 2-6, appendages of prosoma ; 7-12, segments 
of mesosoma ; 13-18, segments of metasoma ; 19, tail-spine. (After Holm.) 
Eurypterids from other deposits the chitinous exoskeleton has 
been altered into a carbonaceous substance, but in the specimens 
from Oesel the chitin is perfectly preserved in its original 
1866-78, and Geol. Mag. 1879, p. 196; 1887, p. 481; 1888, p. 419; 1907, p. 277; 
Peach, Trans. Roy. Soc. Edinb. xxx., 1882, p. 511; Laurie, ibid. xxxvii., 1892, 
p- 151; xxxvii., 1893, p. 509; and’xxxix., 1899, p. 575. 
