98 NEW YORK STATE MUSEUM 
require an identical answer, but the singular association of the two in 
unusual display under peculiar conditions and on both continents strongly 
implies a community of habit, at least at the stages in question. The 
association is one of the most unique [!] faunal and physical combinations 
of geologic history. | 
The earlier occurrence of the eurypterids in marine deposits is almost 
as limited as that of the fishes, and yet they were well adapted to fossil- 
ization and were actually fossilized as far back as Precambrian times, as 
Walcott has recently shown by their discovery in the Belt Mountain terrane 
of Montana. Of about a dozen known genera of eurypterids, only two 
or three of those least well known are without associations with forma- 
tions regarded as fresh water. The relics found in marine sediments may 
be attributed to transportation from the land just as is done in the case 
of the terrestrial plants and land insects not infrequently found in marine 
beds; but transportation in the opposite direction can not be assigned 
. . . From the occurrence of eurypterids first in marine beds apparently 
and later in fresh-water deposits it has been inferred that they were orig- 
inally sea dwellers and later became adapted to land waters, but the 
meagerness of their marine record on the one hand, and their abundance 
and fine preservation in the fresh-water deposits on the other give point 
to the question whether their early marine record is anything more than 
the chance deposit of river forms borne out to sea. 
In view of the contrasting opinions which have been thus expressed 
as to the original habitat of the eurypterids, it will be well to analyze 
closely here the evidence from the rocks which contain the eurypterids, 
and from the associated species. 
In regard to the Cambric Strabops thacheri, the Lower 
Siluric Echinognathusclevelandi and Megalograptus 
welchi, the Clinton Eurypterus prominens and the Guelph 
E. boylei, we might concede, in view of the fact that all these remains - 
have been found in only a single individual each, that they are remains 
carried out to sea from terrestrial waters, yet their combined evidence 
inclines to the side of the marine habitat. 
The profuse Lower Siluric (Frankfort) fauna is associated with sea- 
weeds, graptolites, trilobites, cephalopods and brachiopods, and inhahi- 
ted the pools of a littoral region with abundant detrital sediments. All 
