Palaeozoic Arachnida of North America. 121 



the others recurved. The sixth tergite somewhat longer than the 

 preceding, but its posterior edge not thickened. Anal operculum round, 

 impressed clearly on the dorsal surface ; the reverse does not show it 

 because the end of the abdomen is chipped off. Sternites not visible, 

 the tergites appearing as clearly on the ventral surface as on the dor- 

 sal, only reversed, i. e. what appears as a groove on the dorsal 

 surface has a counterpart in a ridge on the ventral surface. 

 Only the first sternite is clearly visible, small, triangular. 



Fig- 75- Fig. 76. 



Figure y^.—Discotarbus deplanahis n. sp., holotype, Peabody Mus. No. 174, 

 showing the cephalothorax and abdomen. Figure 76. — Same, ventral sur- 

 face. X Y 



Sternum long, divided into three areas of which the middle one is 

 hexagonal, the other two pentagonal. Coxae of pedipalpi wedge- 

 shaped, contiguous throughout their entire length. Coxae of first 

 pair contiguous at base. Coxae of fourth pair of legs 1^/3 as long as 

 those of the first pair. Trochanters one-jointed. Legs short. Pa- 

 tella of first leg longer than femur. Patella and femur of third leg 

 with a distal posterior process. Whole body quite flat and smooth, 

 apparently covered with a thin layer of graphite. 



Total size of specimen No. 175, 23.5 mm. Cephalothorax 9.0 mm. 

 long, II. o mm. wide between the posterior corners. 



Found in the Pennsylvanic (LoM^er Allegheny) of Mazon Creek, 

 Illinois. 



Metatarhus n. gen. 



Cephalothorax triangular, with posterior corners rounded. Pos- 

 terior edge procurved. Eyes absent. Only four anterior abdominal 



