CARBONIFEROUS ARACHNIDA OF NORTH AMERICA. 451 



terminal snbsegmcnt riiii.s down the middle of the abdomen, but thei-e is no sign of any 

 lateral suleation as in neighboring genera. I have left in the figure the knob-like ap- 

 pendages mentioned above at the outer base of the apical sul)segments of the abdomen, 

 drawn by the artist, but I believe them to be purely accidental and perhaps wholly foreign 

 to the creature as they ai'e really distinctly pi'esent only on one side as a mere depi'es- 

 sion. 



Length of body, 11.5 mm. ; width of cephalothorax, 4.5 mm. ; length of abdomen, not in- 

 cluding terminal segments, 7 mm.; its width, 4.75 mm.; width of terminal subsegment, 

 1.25 mm.; length of legs (imperfect) beyond body, 13 mm.; their width, 0.3-0.5 mm. 



Mazon Creek, 111. Mr. K. D. Lacoe, No. 1756 ab. 



Anthracomaetus Karsch. 



Antliracomartus Karsch, Zeitschr. deutsch. geol. Gesellsch., 1882, 560 (1882). 



Cephalothorax quadrate, the front square, or scarcely convex, about half the size of 

 the abdomen; the coxae laterally affixed, radiating from a broad triangular sternal plate, 

 the base of which forms the posterior margin. Sides of the body showing a distinct 

 though slight constriction between the cephalothoi-ax and the abdomen by the more con- 

 vex sides of the latter. Abdomen orbicular, a little longer than broad, composed of seven 

 segments of similar length. 



This is apparently the most abundant type of Arachnida in the carboniferous foinna- 

 tion. Knsta has found four oi- five species in Bohemia alone, one is found in Silesia, an- 

 other in Belgium, and at least two in our own coal. These last are described below. 



Anthracomartus trilobitus. 



PL 39, figs.7-10. 



Anthracomartus trilohitus Scudd., Proc. Amer. Acad. Arts Sc, xx, 17 (1884) ; Comp- 

 tes rend. soc. ent. Belg., (3) No. 62, p. 85, fig. (1885). 

 Although more than half a dozen specimens of this sjjecies have been obtained, the ab- 

 domen is the only part that has been secui-ed in a complete condition, the cephalothorax 

 being incomplete if present, and the appendages in no case present. It offers, however, 

 sti'iking differences from the other species known. The cephalothorax was hexagonal in 

 outline, the front and hind margins forming the longest and subequal sides, and the lateral 

 margins being roundly angulated behind the middle, the hinder lateral margins formed 

 the shortest sides of the hexagon; the front is nearly straight, slightly convex, and a lit- 

 tle longer than the straight or even slightly concave hind margin; the surface is near- 

 ly flat but slightly domed, with the transversely ridged hinder margin separated from 

 the main mass by a straight transverse furrow. The abdomen is very broad and well 

 rounded, excepting in front where the extremely broad base is almost straight, gen- 

 tly convex, and on each side extends far beyond the cephalothorax, being even here, 

 where the abdomen is narrowest, wider than the widest part of the cephalothorax; 

 and as the hinder poi-tion of the cephalothoi-ax rapidly narrows backward, an unus- 

 luvlly deep excision separates it from the abdomen. The outer angles of the base of 



