Palaeozoic Arachnida of North America. 



47 



of preservation of the only existing specimen makes it impossible 

 to recognize the shape of the sternum or the position of the coxae. 

 Genotype T. americanus n. sp. 



Trigonoscorpio americanus n. sp. 

 Plate IV, figs. 17, 18; text fig. 10. 

 The nodule containing the type specimen consists of two parts, 

 but both show the same structure, so that we have before us a cast 

 and mould of the dorsal surface. 

 The cephalothorax has an almost 

 triangular shape, being 5 mm. 

 wide at the posterior edge and 

 only 1.17 mm. at the anterior edge. 

 Its length in the middle line is 

 4.8 mm. Its shape is best under- 

 stood from the text figure 10. 

 The eye tubercle is close to the 

 anterior edge and carries two 

 oval eyes. Two sulci run from 

 the sides of the eye tubercle 

 backward uniting in a transverse 

 sulcus. Another shallow sulcus 

 runs transversely close to the 

 posterior edge. The abdomen 

 is II. 5 mm. long. The first tergite 

 is the longest and the seventh 

 the shortest, being almost com- 

 pletely fused with the sixth. 

 The post-abdomen is compara- 

 tively short and slim. Its fourth 



Fig. 10. 

 Figure lo. — Tri(;onoscorpio americanus 

 n. sp., holotype, Daniels coll., dorsal 



surface. 



X 



3 



segment is 2-''/4, and its fifth 3^/4 

 times as long as wide. The whole 

 body is very flat and smooth. 

 The right pedipalp is complete but for the middle of the femur the 

 ends of which are, however, well outlined. The femur is 5.7 mm. 

 long, patella 2.9 mm., tibia with finger 6.0 mm. Both mandibles 

 are well preserved. Of the legs one can see three pairs on the right 

 and four on the left, but none of them is complete. The complete 

 length of this specimen, which is in the collection of Mr. L. E. Daniels 

 of La Porte, Indiana, is about 25 mm. It was found in the Penn- 

 sylvanic (Lower Allegheny) of Mazon Creek, Illinois. 



