108 Alexander Petrunkevitch, 



their proximal end. Between them two triangular plates, probably 

 chelicera. Sternum long and narrow, with three pairs of lateral 

 processes, an anterior median, trifid lobe and a posterior bifid lobe. 

 Trochanters one-jointed. Pedipalpi missing. Faint impressions of 

 the third left and second and third right legs. Femur of fourth pair 

 of legs 4.6 mm. long. Anal operculum round. The segment sur- 

 rounding it much wider than long. Abdominal sternites recurved, 



Fig. 65. 

 Figure 6s- — Trigonoiarbns carhonarius n. sp., holotype, U. S. N. M. 

 37978, ventral surface as it appears on the nodule. X -r- 



eight in number. Abdomen almost hemispherical in a transverse 

 section, probably spherical in life. 



Found in the Pennsylvanic (Lower Allegheny) of Mazon Creek, 

 Illinois. 



ORDER OPILIONES 



Head completely fused with thorax. Abdomen broadly joined 

 wath cephalothorax, composed of ten segments ; the anal operculum 

 placed ventrally represents the tergite of the tenth segment. 

 One pair of eyes, sometimes e3'es absent. Chelicera three-jointed, 

 chelate. Pedipalpi pediform. Trochanter usually one-jointed. 

 Patella present in all legs. Coxae of first pair of legs and often of the 

 second and third with maxillary lobes. Respiratory organs in the 

 form of tracheal tubes with one pair of spiracles either on the second 



