Page:The Eurypterida of New York Volume 1.pdf/222

 The fourth specimen is very fragmentary, poorly preserved and recognizable as belonging here only by the presence of the terminal spines of the paddles.

bears some similarity to  in the squarish outline of its carapace and the proportions of the carapaces and preabdomina. It was not so well adapted to swimming as is shown by the less developed and more slender swimming legs and the presence of a terminal spine, obviously used in walking, and also by the shorter and stouter postabdomen. While the species may have been a less active swimmer, the extremely broad doublure of the carapace may indicate an adaptation of the front edge to shoveling or digging.

This subgenus is proposed for the species,, described by Whiteaves from the Guelph formation of Ontario; a form which exhibits a number of characters that show it to be an aberrant type distinctly adapted to the peculiar conditions of the Guelph sea. These special traits are found in the thick integument of carapace and abdomen which apparently was not only chitinous but calcareo-chitinous; the highly raised lateral margins of the carapace and the presence of elevated and divided knots on the second to fifth tergites.

The extraordinary thickness of the test is shown not alone in the wholly uncompressed condition of the carapace but more in the fact that, though the abdomen has been shoved forward so that the segments are pushed into each other like joints of a telescope, they have not suffered from crumbling or folding as they always do in the other eurypterids and their greatly thickened posterior edges stand out freely. The front margin of the carapace forms a broad beveled shoveling edge, while the lateral margins are much thickened and elevated into prominent ridges. The abdomen seems to have been very compact and short, as shown by the relatively short last two postabdominal segments. The telson spine is