2 20 THE HABITAT OF THE EURYPTERIDA 



acteristics of a Bertie species. The evidence is frail, and yet it might 

 seem a little disconcerting to have an individual which came from 

 Appalachia, as we think, showing relationship to one coming from 

 Atlantica, but I shall have a suggestion to make when I come to the 

 Bertie that will do away with even this slight difficulty, which is, 

 after all, entirely negligible, since the only specimen showing relation 

 to a Bertie form is a single metastoma which bears only a suggestion 

 of similarity. Continuing in chronological sequence, the next forma- 

 tion in which a Dolichopterus occurs is the Shawangunk grit where 

 there are two species D. otisius with a large representation of carapaces 

 none of which retain more than two body segments, and D. stylonu- 

 roides of which three carapaces and one more complete individual have 

 been found. The former species has certain characters in common 

 with D.macrochirus (Bertie), the young of both being even more alike 

 than the adults. If the two species are phylogenetically related, 

 then the adult D. macrochirus has kept the ancestral characteristic of 

 a broad frontal lobe on the carapace, for this is found in the young of 

 both species and retained throughout the ontogeny of the Bertie 

 form, while D. otisius in the adult shows a development of this lobe 

 into an angular extension. In this one characteristic, then, D. mac- 

 rochirus would show retardation. The second species in the Sha- 

 wangunk is rare and shows no close relationship to any known species. 

 In considering both the Schenectady and Shawangunk faunas, we 

 have seen that there was a species of Dolichopterus in the latter and 

 a single specimen in the former which showed a more or less close 

 relationship to certain species of the same genus in the Bertie. From 

 purely stratigraphic reasoning it is known that specimens of the first 

 two formations were derived from Appalachia, while those of the Ber- 

 tie came from Atlantica. The question might be raised whether the 

 stratigraphic facts do not conflict with my biological theories, for I 

 have been trying to show that eurypterids found in sediments which 

 were transported by rivers on the same continent should show genetic 

 relationship and should for the most part be distinct from those which 

 lived in rivers on different continents; but the species of Dolichopterus 

 do not seem to conform to this law. In the case of this particular 

 genus with its distribution in time, there would be no apparent physi- 

 cal objection to the accounting for its affinities on the very simple as- 

 sumption that the Cambric or earlier generic ancestors lived in rivers 

 either on Appalachia or on Atlantica and that during one of the peri- 

 ods when these continents were connected by a strip of land the eu- 



