112 Alexander Petritnkevdch, 



text figure 69, the demarcation lines are quite clear, but beyond the 



seventh sternite they become faint. Probable number of sternites 



eleven. Coxae visible only at their distal ends. Sternum obliterated. 



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



Illinois. 



ORDER HAPTOPODA 



Head completeh' fused with thorax. Abdomen broadly joined \vith 

 cephalothorax, composed of eleven segments. Pedipalpi short, pedi- 

 form. Terminal segment of the first pair of legs seven-jointed, modi- 

 fied into a tactile organ. Coxae without maxillary lobes. 



This order is so closely related to the Phalangiotarbi, that it seems 

 to have been more reasonable to place the only genus and species 

 known in a separate family under the latter order. The segmentation 

 of the first tarsus is about the only character of importance sepa- 

 rating the two Orders. Yet we must not forget that in the order 

 of Solifugids for example the tarsus shoes a different number of 

 joints in closely related genera. That the seven-jointed tarsus of 

 Plesiosiro madeleyi is a tactile organ is a hypothesis which can be 

 neither substantiated nor disproved. However, since I have not 

 seen any specimen of the only known species, I have retained 

 Pocock's order and refer the reader for details to his Monograph. 



Family Plesiosironidae. 

 Genus Plesiosiro Pocock 191 1. 

 -I. P. madeleyi Pocock, Carb. Arachn., 1911, p. 44, pi. II, fig. 5, text 

 figs. 15, 16. 



Found in the Coal Measures of Coseley, near Dudley, England. 



ORDER PHALANGIOTARBI 



Head completely fused with thorax. Abdomen broadly joined 

 to the cephalothorax. Pleurae soft, without sclerites, not segmented. 

 Several anterior abdominal tergites very short, with a thickened pos- 

 terior edge. Chelicera not known. Pedipalpi short, pediform. 

 Coxae without maxillary lobes. All trochanters one-jointed. Patella 

 always developed. Anus subapical or ventral in position, closed b\' an 

 operculum. Abdomen composed of ten to twelve segments. Eyes, 

 when present, in the number of two on the cephalothorax. 



