round or tubular instead of flattened into a paddle; and the ninth segment forms a strong claw corresponding to the size of the whole leg. The legs form together a series that increases regularly in length backward, and the first four pairs are spinous. The carapace is large, the body slender and the telson distinctly styliform.
Laurie [1899, p. 582] has shown that his genus Drepanopterus differs from Stylonurus only by a negative point of chief generic importance, namely, the fact that its last pair of appendages are not excessively elongated, and he states that Stylonurus developed from Eurypterus by way of forms most nearly represented by Drepanopterus, in which there was greater specialization of the fifth appendage, and reduction of the sixth appendage from the typical digging leg to a purely crawling one. The Otisville material and some of Laurie's drawings indicate that in Stylonurus the second and third pairs of legs are also much elongated and specialized by the multiplication of the spines and by their development into broad lobes in species such as S. excelsior [see restoration plate 47]. The body has become still more slender and the slender form of the telson has given the genus its name.
Stylonurus alone of the whole branch has lived into the Devonic era, attaining there immense proportions. It represents an extreme of specialization that is strongly contrasted to that of the Pterygotus branch.
The main stem represented by Eurypterus has persisted with little change into the Carbonic and even into the Permic. The prevailing expression of Eurypterus in the Carbonic is, however, that represented by the subgenus Anthraconectes. We have elsewhere fully shown that the species referred to this group exhibit distinct phylogerontic characters in the excessive spinosity of the body due to the development of the "scales" into spines, in the elongation of the epimeral pieces and in the excessive length of the telson.
A small independent branch that came off from Eurypterus is represented by Eusarcus. In its triangular carapace, anterior eyes, broadly
