also short and thick. The surface of the carapace exhibits in front an unusual sculpture consisting of intricately mingled short, coarse, curved ridges of confluent tubercles. On the posterior part of the carapace the tubercles are mostly separated. The axial knots on the segments were solid bodies. All these features combined demonstrate that the integument of this subgenus was not merely chitinous as in the typical Eurypterus, but much strengthened by calcareous deposits which became most prominent in the sculpture of the carapace and in the knots of the tergites.
Figure 43 Tylopterus boylei (Whiteaves). Holotype refigured in natural size, and enlargement of sculpture of carapace
This thickening of the carapace is entirely in accord with the character of the Guelph fauna described by the authors from New York, where the fact of the peculiar thickening of the shells in all classes, notably the brachiopods and mollusks, has been emphasized and been ascribed to the strongly saline water and in part to the life of the organisms on wave-beaten coral reefs. Tylopterus boylei seems to be an adaptation to the same peculiar conditions which are also indicated by the character of the matrix of the fossil, a porous, coarse-grained dolomite.
It would suggest itself to compare this species with the Carbonic eurypterids described by Etheridge (E.? stevensoni, see text fig. 48) and Woodward (E. scabrosus) in which the integument has become greatly thickened by deposition of globular calcite ("calculi"). We have in another place considered these features as phylogerontic in the Carbonic subgenus Anthraconectes and as due to the waning vitality of the race. It is hardly to be assumed that the characters of the Siluric T. boylei are due to the same gerontic conditions and that the latter is an ancestor of the Carbonic Anthraconectes. It would
