of the genus and in this evidence of waning racial characters it invites special recognition. The Pennsylvania species to which we have referred are E. mansfieldi C. E. Hall, E. pennsylvanicus C. E. Hall, E. stylus J. Hall and E. approximatus Hall & Clarke.[1] These species, together with E. (Anthraconectes) mazonensis are distinguished from Eurypterus proper by the following features: (1) the character of the spines of the endognathites,[2] seen in E. mansfieldi, in E. mazonensis and E. stylus,[3] (2) the development of the scales into mucros, giving the greater portion of the surface a spinous appearance. This tendency to spinosity, especially of the posterior 
Figure 48 Eurypterus (?) stevensoni Etheridge. Spines and scales. (From Etheridge) margins of the abdominal somites is also present in British Carbonic forms, as is amply evidenced by E. scouleri Woodward[4] with its long pointed scales, E. (?) stevensoni R. Etheridge jr [Geol. Soc. Lond. Quar. Jour. 1877. 33:223] in which the surface is covered with long blunt spines and scales, giving it the appearance of a mass of congealed drops, while in E. scabrosus H. Woodward[5] the scales have become prominent wartlike tubercles, interspersed with disklike bodies which proved to be "calculi" or bodies of globular calcite formed inside the integument. All these excrescences are distinctly phylogerontic and seem to indicate that
- ↑ The first two are described in the Proceedings of American Philosophical Society, volume 7, 1877, and Second Geological Survey of Pennsylvania, Report of Progress, PPP, 1884, page 31 et seq. E. stylus is described in the last named publication and E. approximatus in the Palaeontology of New York, volume 7, 1888, explanation of plate 27, figure 6. E.potens Hall is not described and the figures [Penn. Rep't, pl. 4, fig. 9, 10] indicate that it is based on unrecognizable fragments.
- ↑ See Appendix.
- ↑ In E. pennsylvanicus and E. approximatus the endognathites are not preserved. The former species is based on a single carapace.
- ↑ Pal. Soc. 1872. v. 26, pl. 25–27.
- ↑ Geol. Mag. n. s. 1887. dec. 3, 4: 481.
