maxillary lobes of second pair of legs similar to Phalangium ; the skin 



Our species of this genus are picius and ohioensis. 

 The two western species described by Dr. H. C. Wood as Phalangium 

 favosum and P. nigrum which on account of their hard skin I have 

 heretofore referred with some doubt to the sub-family Sclerosomatina? 

 prove not to belong there, as I learn from Dr. T. Thorell to whom I 

 submitted specimens, and who writes that they represent undescribed 

 genera. It seems to me that they differ sufficiently from the Phalangi- 

 ime to form a distinct subfamily. For P. favosum I have erected the 

 genus Trachyrhinus, which is characterized as follows : 



Body very hard : dorsum a large plate with a rough, coarsely 

 punctate surface. Front margin of cephalothorax furnished with two 

 denticulated tubercles. Eye eminence prominent with two rows of 

 large tubercles having spinose tips. Legs rather long, thickly beset 

 with spinose tubercles. Pores on margin of cephalothorax rather 

 small, oval. Palpal claw smooth ; inner distal angle of femur very 

 slightly, and of patella quite strongly developed. First joint of 

 mandible furnished with a tooth on lower surface. 



One species Trachyrhinus favosus (Wood) inhabiting the Western 

 States. 



The P. nigrum of Dr. Wood may serve as the type of the new genus 

 Mesosoma, having the following characters : 



Dorsum a firm hard plate thickly studded with small hemispherical 

 tubercles. Eye eminence of nearly equal height, length and breadth, 

 covered with similar tubercles, and not carinated. Palpi moderately 

 robust not branched, and furnished with many tubercles ; palpal claw 

 pectinate. Tooth on underside of first joint of mandibles. Legs short, 

 coriaceous, robust. Lateral pores on upper margin cephalothorax 

 very distinct, subcircular. 



One species, Mesosoma nigrum, found in the western and south- 

 western States. It is possible that the western form described by 

 Wood may be different from Say's species. The latter records his 

 species as common in Georgia and the Carolinas, but I think none 

 have since been reported from this locality. 



These two species belong neither to the Phalangiinse nor the Sclero- 

 somatinoe as now restricted by European authors, having some 

 characters of each. They apparently form a new sub-family which 

 may be called the Mesosomatinse, and be defined as follows : 



Body very hard, most of the dorsal segments being united in a firm 

 dense plate. Posterior dorsal and the ventral segments having their 



