120 



Alexander Petrunkevitch, 



patellae without apical process. Text figure 74 shows all legs as 

 they appear on the reverse. The majority of specimens have only 



fragments of legs. Dorsal 

 surface of abdomen appe- 

 aring also on the reverse. 

 Abdomen smooth. Legs 

 and distal ends of coxae 

 distinctly punctate. 



Found in the Pennsyl- 

 vanic (Lower Allegheny) 

 of Mazon Creek, Illinois. 



Discoiarbus n. gen. 

 Cephalothorax triangular 

 with strongly procurved 

 posterior edge and curved 

 sides. Posterior corners 

 angular. Abdomen round 

 and very Wide ; of the five 

 short tergites with heavily 

 thickened posterior edge, 

 the first three are procur- 

 ved, the fourth and fifth 

 straight. The sixth ter- 

 gite is short, but without 

 thickened edge. Sternum long, divided into three areas of which 

 the middle one is hexagonal and the other two pentagonal. Body 

 very flat. Genotype D. deplanatus n. sp. 



Figure j^.—Geratarbus miniihis n. sp., holo- 

 tjpe, Peabody Mus. No. 176, dorsal view 

 of cephalothorax and abdomen. Figure 

 74. — Same, ventral surface with legs. X -r 



Discotarhus deplanatus n. sp. 

 Plate XII, fig. 10 ; text figs. 75, 76. 



Two specimens, Nos. 174 and 175, in the Peabody Museum. The 

 first is twice as small as the second, but better preserved. Since 

 the larger specimen shows the same structure there is no reason for 

 separating it into another species. I choose the smaller specimen, 

 No. 174, as holotype. 



Type specimen. Total length 11.25 rnm. Cephalothorax 4.5 mm. 

 long, 5.12 mm. wide between the posterior corners. Posterior edge 

 strongly procurved. Sides curved. Eyes absent. Five anterior 

 tergites very short, with heavily thickened posterior edge. First, 

 second and third tergites procurved; fourth, fifth and sixth straight; 



