The succession of habitats is hence, according to our evidence, the reverse of that suggested by Chamberlin's hypothesis noted at the beginning of this discussion.[1]
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 Otisville 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[2] of Limulus and probably
- ↑ 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. 10, 11] as egg packets (Parka decipiens) of Pterygotus ludensis, masses of small, oval carbonaceous bodies of frequent occurrence in the basal Old Red sandstone. 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 waterlime 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.
