CHAPTER xt 
ARACHNIDA (CON TINUED)——DELOBRANCHIATA = MEROSTOMATA 
(CONTIN UED)—EURYPTERIDA 
\ 
Order II. Eurypterida. 
THE Eurypterida or Gigantostraca are found only in the 
Palaeozoic formations. Some species of Pterygotus, Slimonia, 
and Stylonurus have a length of from five to six feet, and are 
not only the largest Invertebrates which have been found fossil 
but do not seem to be surpassed in size at the present day except 
by some of the Dibranchiate Cephalopods. All the Eurypterids 
were aquatic, and, with the possible exception of forms found in 
the Coal Measures, all were marine. The earliest examples 
occur in the Cambrian deposits, and the latest in the Permian ; 
but although the Eurypterids have thus a considerable geological 
range, yet 1t is mainly in the Silurian and the Old Red Sand- 
stone that they are found, the principal genera represented in 
those deposits being Hurypterus, Stylonurus, Slimonia, Pterygotus, 
Hughmilleria, Dolichopterus, and Eusarcus. From the Cambrian 
rocks the only form recorded is Strabops;' in the Ordovician 
the imperfectly known Zehinognathus” and some indeterminable 
fragments have alone been found, In the Carboniferous deposits 
Eurypterus and Glyptoscorpius occur, and the former survived 
into the Permian.’ 
1 Walcott has described, under the generic name Beltina, imperfect specimens 
from the Algonkian (pre-Cambrian) of Montana, which he thinks may be the 
remains of Eurypterids (Bull. Geol. Soc. America, x., 1899, p. 238). 
2 Walcott, Amer. Jowr. Sci. (8), xxiil., 1882, p. 213. 
* Descriptions and figures of British Eurypterids are given in the following 
works :—Huxley and Salter, ‘‘ Pterygotus,” Mem. Geol. Survey, Brit. Org. Re- 
mins, i., 1859 ; H. Woodward, ‘‘ Monograph of the Merostomata,” Palaeont. Soc. 
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