Palaeozoic Arachnida of Xorth America. 117 



Family Phalangiotarbidae. 

 JSiew definition. Coxae of pedipalpi wedged in between the coxae 

 of the first pair of legs, narrow and long, contiguous throughout their 

 entire length. Sternum oval or elongated, mth the coxae of the legs 

 radiating from it and increasing in length from the first to the fourth. 

 Trochanters of the first and second leg always one-jointed. Patella 

 developed. Legs all short and stout. Abdominal tergites, not count- 

 ing the ventrally placed operculum anale, ten. The first five or four 

 tergites very short with heavily thickened posterior edge appearing 

 in the specimens as a deep groove. Genital opening on the first 

 sternite. Pleurae soft, not segmented. 



Key to the Genera of Phalangiotarbidae. 



1. Posterior edge of the cephalothorax straight or very shghtly 

 procurved. The first 5 abdominal tergites straight or almost 



straight 2 



-h posterior edge of the cephalothorax strongly procurved. The 



first 2 or 3 tergites strongly procurved 3 



2. Coxae of the ist pair of legs completely separated by the coxae 

 of the pedipalpi. Coxae of the 4th pair far apart 



Phalangiotarhus 

 + Coxae of the ist pair of legs contiguous at their base. Coxae 

 of the 4 th pair approximated 



Geratarhus 



3. Abdomen disc-shaped, quite flat. Posterior corners of the cephalo- 

 thorax angular 



Discotarhus 

 + Abdomen oval. Posterior corners of the cephalothorax rounded 



Metatarhus. 

 Genus Geratarhus Scudder. 

 New definition. Coxae of pedipalpi wedge-shaped, coxae of first 

 pair of legs contiguous at base. Posterior edge of cephalothorax al- 

 most or quite straight. Anterior five abdominal tergites straight, the 

 following very slightly recurved. Sternum oval. Abdominal stern- 

 ites divided into three fields by longitudinal lines. Genotype 

 G. lacoei Scudder. 



Key to the Species of Geratarhus. 

 I. Cephalothorax with parallel sides and broad anterior edge 



G. lacoei 

 + Cephalothorax -with rounded sides converging anteriorly to a 

 sharp point 



G. minutus. 



