Page:The Habitat of the Eurypterida.djvu/229

Rh were widely dispersed on both continents; the later consanguinity is thus easily understood. But I think that such an assumption is unnecessary and my reason will be readily apparent when we consider the Bertie species of Dolichopterus, D. macrochirus, D. testudineus and D. siluriceps. The relationship of the first to a species in the Shawangunk has just been discussed. Concerning the second, Clarke and Ruedemann remark: "This species, as represented by the single carapace, is quite similar to D. otisius. It differs from the latter mainly by the greater extension of the frontal portion and by the more pronounced posterior contraction of the carapace. The frontal transverse ridge or fold observed in the species is also seen in D. otisius" (39, 275). If the two species were genetically related, this more pronounced extension of the frontal portion of the carapace would be predicable in the Bertie species, for according to the laws of recapitulation and tachygenesis a morphological character found in the adult of any species will appear at an earlier and earlier stage in the ontogenetic development of its descendants, and since the apparently orthogenetic tendency in the Shawangunk species D. otisius showed a progressive modification from rounded to angular and extended frontal margin, the late Bertie species D. testudineus should show a more protruding frontal rim than is found in the adult D. otisius. The third Bertie species is D. siluriceps of which a single poorly preserved carapace is known, and which cannot be compared to any other species save a small form from the Shawangunk. The genus Dolichopterus is not known from any other country, nor has it been found in beds of later age than the Bertie. Even the three species in the Bertie are so poorly represented that one wonders what happened to the fauna. Of the genotype, D. macrochirus, four incomplete though excellently preserved specimens are extant; of each of the other two species there is a single carapace. If these eurypterids lived in the Bertie "pools" of authors, it is inconceivable that not more individuals (or exoskeletons) should have been preserved; if they lived in the rivers coming from Atlantica, this scarcity is accounted for. But the study of the phylogeny of this genus leads me to think that Dolichopterus was confined to the rivers of Appalachia throughout its whole racial history. (Its occurrence in so fragmentary a condition in the Bertie suggests that the few remains were transported from the debouchure of some river of Appalachia and carried into the Bertie muds). There is as yet too little evidence, too many pages in the history are still unread, for a reasonably