THE EURYPTERIDA OF NEW YORK 85 
great exterior similarity of the eurypterids and ostracophores and the 
explanation of this phenomenon as resulting from adaptation to like con- 
ditions. The ostracophores have been generally regarded by paleontol- 
ogists. as owing their peculiar form to their mud-grubbing habit, and it 
may be inferred that the eurypterids, being of similar form, were of like 
habit and perhaps of like form because of similar habit. 
III 
GEOLOGICAL DISTRIBUTION AND BIONOMIC RELATIONS 
In this chapter we shall first survey the geological distribution of the 
eurypterids in North America as indicated by the following conspectus, com- 
pare this distribution with that in Europe, and finally attempt a conclusion 
as to the physical conditions under which these strange creatures lived. 
A Conspectus of American species arranged according to their geological 
occurrence 7 
Algonkian 
Beltina danai Walcott. Greyson shales, Montana 
Camobric' 
Strabops thacheri Beecher. Potosi limestone, St Frangois county, Missouri 
1 There occur gigantic tracks in the Potsdam rocks of New York which, have been 
considered by good authorities as suggesting the presence of merostomes at that age. 
These tracks known as Climactichnites, were first described by Logan [Can. Nat. & 
Geol. 1860. v. 5] and later recorded by Hall [N. Y. State Mus. 42d Rep’t. 1889. p. 25] 
from Port Henry, Essex co., N. Y., and by Woodworth [N. Y. State Mus. Bul. 69. 
1903. p. 959] from the town of Mooers, Clinton co., N. Y. In the latter locality 
they assume gigantic proportions, being 6 inches wide and 15 or more feet long, 
terminating in an oval impression 16 inches long. 
. Various explanations have been suggested for these tracks. Besides having been 
referred to trilobites, burrowing crustaceans, plants, gastropods and annelids, they 
have been cormnpared with those of the horseshoe crab, first by Dawson and recently 
again by Hitchcock and Patten. Sir William Dawson [Can. Nat. & Geol. 1862. 
7: 271], who studied the American Limulus on the seashore, pointed out that when 
Limulus creeps on quicksand, or on sand just covered with water it uses its ordinary 
walking legs and produces a track strikingly like that described as Protichnites 
from the Potsdam sandstone, but in shallow water just covering the body, it uses 
its abdominal gill plates and produces a ladderlike track the exact counterpart of the 
