Page:Second Geological Survey of Pennsylvania Report of Progress PPP.djvu/47

 very long, being six times as long as wide; the extremity is divided into four lobes, two of which form the extremity proper, while the other two are just anterior thereto. The lobes are triangular, and the anterior pair are ornamented with five or six strong plications. In the angle between the distal pair is a short process which may be the point of attachment of a small terminal appendage. Other parts of the epistoma unknown. Two of the maxillæ have been observed in position; they do not differ conspicuously from other described forms of the genus.

Metastoma ovate, bilobate at the smaller end.

Surface ornamented with minute imbricating scales. On the posterior tergal portion of each somite the scales are larger and triangular. The lateral processes of the first six segments and lateral margins of the carapace are marked by sharp, oblique striæ. The processes of the posterior segments are nearly free from ornamentation, being sometimes marked by one or two striæ. The telson appears to be free from the characteristic ornamentation of the other portions of the test. On the metastoma the scales are larger and more irregular than on the segments.

A large and nearly entire individual has the following dimensions: Extreme length from the anterior margin of the carapace to the extremity of the telson, 228 mm.; length of carapace, 31 mm.; width of fourth somite, 53 mm.; width of last somite, 15 mm.; length of telson, 80 mm. The smallest specimen observed has a length of 83 mm., of which 30 mm. belongs to the telson.

This species differs from E. stylus, with which it is associated, in its greater size, so far as observed, the more elongate form of the carapace, more approximate eyes, shorter palpi, and comparatively much shorter and more slender telson. The caudal spine of E. Mansfieldi is usually about one-third the length of the entire animal, while in E. stylus it occupies nearly-one half of the entire length.

E. Mazonensis, M. & W. from the coal measures of Illinois, bears a close resemblance to this species in general form and surface ornamentation, but the carapace is shorter and more regularly rounded. 3 PPP.