CARBONIFEROUS ARTHROPOD FAUNA I 83 



tures much finer and denser than in sulcata. Legs vaguely indi- 

 cated as scattered fragments. What remains shows them to 

 have been excessively long and slender; the strong flexure at 

 the coxal joints and the absence of the middle parts of the legs 

 would indicate that the body was carried much as with the Pha- 

 langidae of today. 



Length of body 14™"", length of abdomen 9™", breadth 

 of abdomen (approximate) 7°"°, breadth of cephalothorax 

 (approximate) 5™"*. 



Mazon creek, Illinois. Carboniferous. 



Type. Pal. Coll. No. 9236. 



This genus possesses some of the characters of the Anthra- 

 comarti and some of the true spiders. The formation of the coxal 

 plates is quite suggestive of the former order, while the peculiar 

 segmentation of the abdomen — the basal segments being as 

 large or larger than the apical — and the possession of what are 

 possibly spinning organs are equally incongruous for the group. 

 But two true spiders are known from Carboniferous times, both 

 discovered in Europe. The best-known of these, Protolycosa 

 afithracophila F. Roemer, has abdominal appendages and dis- 

 tinctly segmented abdomen. The other, Palaranea borassifolia 

 Fric, is fragmentary, but seems to be devoid of these appenda- 

 ges. Even if the appendages at the end of its abdomen be 

 interpreted as spinning organs, Kustarachne cannot be included 

 with these, as its relationships are closer with the Anthraco- 

 marti, as can be seen by its sessile abdomen and the arrange- 

 ment of its coxae. It would seem as if this genus, of which the 

 three species agree pretty closely, was in the line of descent 

 from the ancestors of both the Anthracomarti and the Araneae, 

 related more closely to the former, but sufficiently removed 

 to be considered now as equivalent to the other genera of the 

 group together. 



Although archaic, Kustarachne is not ancestral. Even at this 

 early period it had attained a certain degree of specialization in 

 the loss of its abdominal legs, the anchylosis of the basal seg- 

 ments of the abdomen, and the peculiar development of its legs. 

 But that it was not so highly organized as its contemporaries 



