Palaeozoic Arachnida of North America. 39 



8.2 mm. in length, 5.5 mm. in breadth ; third, 9.5 mm. in length, 

 4.5 mm. in breadth. They are all oblong in form, more or less nearly 

 rectangular at their ends, and, as near as can be determined from a 

 flattened specimen, apparently provided above with three or more 

 longitudinal rows of granules, and some scattering ones. 



"The single detached comb-like organ, seen lying in the matrix 

 on the left side of the abdomen, shows some eleven or twelve of the 

 little laminae or divisions, but apparently had more, as it is incom- 

 plete, at least at one end." 



It is unfortunate that both the cast and the mould show the dorsal 

 surface of the scorpion. In consequence nothing is known of the 

 shape of the sternum. The total size can also be only guessed and 

 is probably about 90 mm. The specimen was found by Mr. M. 

 Prendel on Mazon Creek, Illinois, in Pennsylvanic (Lower Allegheny) 

 strata. 



Eoscorpius typicus n. sp. 

 Plate I, figures 1—4; text figures 5—7. 



This species is represented by four specimens. Two of these, 

 Nos. 37986 and 37987, are in the U. S. National Museum, and two, 

 Nos. 126 and 127 in the Peabody Museum of i^ale University 

 No. 37986 of the U. S. National Museum I chose for the holotype. 



The obverse of the nodule containing the type specimen (PI. I, 

 fig. 2) shows clearly the mandibles, cephalothorax, abdomen, first 

 three segments of the post-abdomen and parts of the right palpus and 

 legs. The reverse (PI. I, fig. 3) shows the complete right palpus, all 

 coxae, sternum, genital opercula, abdomen and four segments of the 

 post-abdomen ; also parts of the legs, as represented in text figure 6. 

 The cephalothorax is almost rectangular in shape, 5.5 mm. long, 

 55 mm. wide at posterior edge. Its posterior edge is quite straight, 

 the anterior one almost straight, with a scarcely perceptible emar- 

 gination. The antero-lateral angles are rounded and the lateral edges 

 distinctly emarginated. Two curved ridges run from the anterior 

 edge, uniting behind the eyes approximately in the middle of the cephalo- 

 thorax, whence a median ridge proceeds almost to the posterior edge, 

 forming here a small triangular field. A pair of curved ridges run 

 from the middle of the lateral edges obliquely toward the posterior edge 

 where they, too, join the triangular field. The median eyes have 

 apparently the shape of segment of a circle, but it is probable that the 

 segment represents only the socket and that the lens iLself Was round 

 or oval. No trace of side eyes could be detected, although the edges 

 of the cephalothorax are very distinct, 



