286 CLAKENCE M. WEED. 



have their margins developed into thin overlapping plates. Pores 

 on margin of cephalothorax distinct. Anal piece unique ; maxillary 

 lobe of palpi with two tubercles. 



The two genera of this subfamily are easily separated by the fol- 

 lowing characters : 



Fourtb legs as long as second legs, or nearly so llesoi^iOllia. 



Fourth legs distinctly shorter than second legs Trachyrhiiiiis. 



MESOSOMA Weed, 189-2. 

 Dorsum a firm hard plate, thickly studded with small, hemispher- 

 ical tubercles. Eye-eminence of nearly equal height, length and 

 breadth; not carinated. Palpi moderately robust, not branched, 

 and furnished with many tubercles ; claw pectinate ; tooth on under- 

 side of first joint of mandibles. Legs short, coriaceous, robust; 

 second and fourth pairs of nearly equal length ; lateral pores on 

 upper margin of cephalothorax distinct, subcircular. 



9Ie<>iOMOina nigriiin (Say) Weed. Plate V. 



Fhalangium nigrum Say, Joitrn. Phila. Acad, vi, p. 66, Compl. Writings, ii, 

 p. 14. Wood, Conim. Essex Inst. vi. p. 34. 



Astrobuniis (f ) nigrum, Weed, Aruer. Nat. vol. xiv, p. 917. 



Mesosoma nigrum. Weed, Amer. Nat. xxvi, 529. 

 Male. — Body 6 mm. long. ; 4 mm. wide ; palpi 4 mm. long. Legs : first, 10 mm. ; 

 second, 17 mm.; third, 11 mm.; fourth. 16 mm. Black; ventrum of cephalo- 

 thorax including coxse, trochanters and base of femora, brown. In some speci- 

 mens the apical portion of the legs, and more or less of the ground color of the 

 dorsum is brownish black. Dorsum thickly studed with small hemispherical 

 black granules or tubercles. Segmentation of abdominal scutum indicated by 

 faint impressed lines. Eye-eminence longer than high, not canaliculate; cov- 

 ered with black tubercles like those on the dorsum. Palpi black, all the joints 

 slightly arched, robust, with none of the angles prolonged ; furnished with more 

 or less scattered black tubercles and spinose hairs ; mandibles blackish. Legs 

 short, robust, granulate; ventral surface of abdomen blackish brown, granulate. 

 Genital organ of male "slender, proximally subcylindrical, then flattened and 

 slightly expanded into a broad, somewhat circular, very thin, alate portion, then 

 suddenly contracted and bent at an obtuse angle, ending in a very fine point." 



Female. — Body 2 mm. long; 5 mm. wide. Palpi 4.5 mm. Legs: first, 10 mm.; 

 second, 17 mm. ; third, 11 mm. ; fourth, 16 mm. Besides its larger size it differs 

 from the male in having less black on the ventral surface, which is cinnamon- 

 rufous, spotted with black ; mandibles brown, black above, and the outer mar- 

 gins of the dorsum of the abdomen smooth without the black tubercles which 

 form a large distinct quadrangular plate on the middle of the abdomen, and a 

 transverse plate on each of the three posterior segments. The smooth margins 

 are brown. 



Described from many specimens. 



Brookings. This remarkable species seems to be rather common 

 in South Dakota. 



