30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



shape is elongate ; it is subparallel with two more or less distinct con- 

 tractions when viewed from the dorsal aspect. The basal portion is 

 semicircular in cross-section, while the anterior, unfused part is 

 strongly compressed. In Gn. rctusus Lee, the ligula is more parallel 

 and the contractions less distinct than in the other species. 



The anterior margin is very feebly, shallowly emarginate or evenly 

 rounded ; however, this does not seem to be constant in individuals 

 of the same species. On the ventral aspect, there is on each side near 

 the anterior margin a row of setae (d). No specific differences have 

 been found either in the shape or in the number of these setae which 

 vary in number from three to seven in each row. The sculpture of the 

 ligula on the ventral aspect in all three species is very much alike, 

 being nearly smooth or feebly transversely wrinkled. Dorsally Gn. 

 retusus shows similar transverse, toothlike wrinkles on the mentum ; 

 the basal portion only is smooth. Gn. matcriarius and sidcatns have 

 the corresponding area smooth with slight indications of transverse 

 wrinkles on the sides. 



Palpi. — The palpi are directed ventrad. Each is composed of three 

 segments, decreasing in size toward the apex. Segments two and 

 three bear dorsally a plush-like arrangement of hairs, while the first 

 joint has a few scattered hairs only. Ventrally, the setae are more 

 sparse and are intermixed with punctures on segments one and two; 

 segment three has no setae but a few punctures. 



Siiuunary of the specific characters: — 



A — Base of the mentum scarcely widened basally, fused with the 

 ligula before the basal margin of the latter; mentum and 

 ligula when seen from above with strongly developed, tooth- 

 like, transverse wrinkles ; ligula subparallel. Gn. retusus I.ec. 



A A — Base of the mentum distinctly widened basally, extending to 

 the basal margin of the labium ; mentum and ligula when 

 seen from below smooth or with slight indications of trans- 

 verse wrinkles ; contractions of the ligula well developed. 

 B — Ventral side of the mentum smooth, with few punctures. 



Gn. sulcatns Lee. 

 BB — Ventral side of the mentum with transverse wrinkles. 



Gn. materiarius Fitch. 



THE THORAX 



The three segments of the thorax, pro-, meso-, and metathorax 

 (figs. I, 2 and 3) are clearly defined in this genus as is usual in this 

 family. Each of these segments has as a basis three primitive ele- 



