Palaeozoic Arachnida of Xorth America. 119 



missing ; of the pedipalpi preserved only the coxae which are wedge- 

 shaped and apparently completely fused together, forming one trian- 

 gular plate. Sternum small, oval. Radiating from it are the trian- 

 gular coxae of the legs. The first coxae are contiguous at their base 

 (apex of the triangle) ; the fourth coxae are 1 1/2 times as long as the 

 first. The first sternite, the only one visible, is large, triangular. 

 Trochanters one-jointed. The third left leg is complete, its femur 

 and patella with an anterior apical process. The second leg shows 

 similar processes in the same joints and in the tibia ; its metatarsus 

 and tarsus are missing. The joints of the fourth leg are without the 

 apical process, metatarsus and tarsus also missing. The body is 

 smooth, the legs are coarsely and distinctly punctate. 



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

 Illinois. 



Geratarhus miniitus n. sp. 

 Plate XI, fig. 69 ; text figs. 73, 74. 



There are altogether six specimens of this species in the Peabody 

 Museum. Their numbers are 176 (type), and 177— 181. 



All are approximately of the same size, their length varying from 

 9.1 to 10.6 mm. Some are of course better preserved than others, yet 

 all show the same structure. No. 176 being the best preserved spe- 

 cimen, I chose it for holotype. 



Body flat. Total length 9.1 mm. Cephalothorax 3.1 mm. long, 

 3.5 mm. wide at posterior edge which is perfectly straight. The sides 

 of the cephalothorax are rounded, converging in front to a sharp point. 

 Its surface perfectly smooth ; eyes absent. The anal operculum 

 round, impressed on both the dorsal and ventral surfaces. Ab- 

 dominal tergites ten. The anterior five short, with heavily thick- 

 ened posterior edge and a median ridge, straight. The following 

 tergites longer, slightly recurved. Pleura not segmented, forming a 

 heavy ridge alongside the abdomen on its ventral surface, anteriorly 

 chipped off exposing the ends of the sternites. Five abdominal stern- 

 ites in front of the last sternite divided by two longitudinal lines into 

 three fields. The triangular area between the hind coxae with an 

 almost round genital operculum divided by a transverse line. Cheli- 

 cera missing. Coxae of pedipalpi wedge-shaped, contiguous throughout 

 their length. Sternum large, longer than wide, with three pairs of 

 lateral projections and a median posterior lobe separating the hind 

 coxae. All coxae with rounded base. Coxae of first pair twice as 

 short as those of the fourth pair, contiguous at base. Trochanters 

 one-jointed. Legs short, but not as heavy as in G. lacoei, femora and 



