THE EURYPTERIDA OF NEW YORK II3 
The succession of habitats is hence, according to our evidence, the 
reverse of that suggested by Chamberlin’s hypothesis noted at the begin- 
ning of this discussion.’ 
The cause of the withdrawal from the sea of these well armed and 
often gigantic eurypterids into the brackish and fresh water is a problem 
‘of much interest. Perhaps the development of the more agile and more 
advanced fishes put these slow and archaic merostomes on the defensive 
and finally forced them altogether out of the sea. Their association with 
clumsy and heavily armed, equally archaic Old Red fishes which clearly 
suffered a like fate from their own more advanced relatives, would seem to 
be very suggestive in this connection. 
It may be mentioned that even the gigantism of these arachnids, as 
typified by Stylonurus excelsior, is probably an indication of 
race degeneracy, as gigantism is generally, and as such is also suggestive 
of their increasing failure to cope with the conditions of marine life. 
IV 
ONTOGENY 
The collections from the shale beds of the Shawangunk grit at Otis- 
ville have furnished an unrivaled series of larval stages of one species each 
of the genera Eurypterus, Pterygotus, Stylonurus and Hughmilleria. Many 
of the growth stages measure but 2 millimeters or even less in length 
and hence so little surpass in size the eggs’? of Limulus and probably 
1 Another consideration which antagonizes that hypothesis is the fact that the 
-brackish fauna, small as it is, as a rule is composed of species which entered the brackish 
zone from the sea and not by such as descended from the fresh-water lakes and the © 
rivers. This has been shown by Walther [Einleitung in die Geologie als historische 
Wissenschaft. 1894. 1 Theil. Bionomie des Meeres] to be especially true of the 
mollusks and crustaceans. 
Henry Woodward described and figured [1872, p. 79, pl. 16, fig. ro, 11] as 
egg packets (Parka decipiens) of Pterygotus ludensis, masses 
of small, oval carbonaceous bodies of frequent occurrence in the basal Old Red sand- 
stone. Dawson and Penhallow [1891] after a careful study of these bodies, concluded 
that they are sporocarps, filled with sporangia, of an aquatic plant. The Bertie water- 
lime and the shale layers of the Shawangunk grit have both furnished circular to oval 
carbonaceous bodies that suggest or are comparable to the eggs of Limulus. 
