CARBONIFEROUS ARACHNIDA OF NORTH AMERICA. 445 



joints are all broken in the specimen, bnt on some of the legs at least were apparently 

 about as long as the second joints ; all the joints are flattened and punctate like the body, 

 but not so deeply. The front pair of legs is about two-thirds as stout as the others and a 

 little shorter. 



Length of body, 15 mm.; ccphalothorax, 6 mm.; first abdominal segment, 0.8 mm.; sec- 

 ond, 2.3 mm.; width of cephalothoivax posteriorly, 5.5 mm.; middle of abdomen, 6.5 mm.; 

 length of second joint of first pair of legs, 4.5 mm.; its width, 0.6 mm.; length of first 

 joint of second pair of legs, 2 mm., its width, 1.9 mm. ; length of second joint of same, 5.5 

 mm., its width, 0.85 mm.; length of first joint of third pair of legs, 2.5 mm., its width, 

 2.25 mm.; length of second joint of same, 6.75 mm., its width, 1.25 mm.; greatest length 

 of any leg (as far as preserved), 10.5 mm. 



Mazon Creek, 111. Mi-. E. D. Lacoe, No. 1745. 



Family Architakboidae Scudder. 



Ccphalothorax variable in form but at least half as large as the abdomen. Coxae ra- 

 diating from a central pit, a median line, or from a broad triangidar space, its base on 

 the abdominal margin. Abdomen orbicular or oval, broad at base with a more or less 

 distinct lateral ridge on each side, converging towai-d the anus; segments from seven to 

 nine in number, visible below, though the basal ones often extremely shortened in the 

 middle; no abdominal a^jpendages. 



This appears to be the best developed among the fomilies of paleozoic Anthracomarti, 

 especially in Ameiica where four genera occur, most of them, so far as known, peculiar 

 to the New World. 



GeRAPHEYNUS Scudder (^y.r/.c,Pl)rynus, nom.gen.). 



Gercvplirynus Scudd., Proc. Amer. Acad. Arts Sc. xx, 16 (1884) . 



Allied closely to Architarl)us; the body is compact Avith no constriction at the sides 

 between the ccphalothorax and alxlomen, agreeing in its general structure with Arch- 

 itarbus, but differing from it considerably in detail. The contour of the body is ovate, 

 but instead of being rounded in front as in Architarbus, it is pointed and angulate, while 

 behind it is also pointed, though roundly. ' The ccphalothorax occupies a little less than 

 half of the body, and the pedigerous coxal segments which, as in Architarbus, are trun- 

 cated wedge-shaped, enlarging distally, meet in a common median longitudinal ridge, 

 the sides of which are rather strongly tectiform; this ridge runs from the extreme front 

 to the posterior edge of the hindmost pedigerous segment, or through about two-thirds 

 the length of the cephalothorax; behind it is the posterior shield of the ccphalothorax, 

 the anterior triangular fi-aginent of which slopes upward to the ridge, while the hinder 

 ])()rtions with their transvei-se scorings and ridgings lie on a plane bt'low. lioth anterior 

 and posterior parts of this shield extend laterally nearly to the borders of the body, and 

 are thus much broader and comparatively shorter than in our species of Architarbus. 



The postthoracic plate is small and resembles thatof Arcliitarbus but is more triangular. 

 The abdomen resembles that of Architarbus rotandatum, since this postthoracic plate, as 



