386 Trans. Acad. Set. of St. Louis. 



Gyrohypnus Steph. 



In this genus the third palpal joint is actually shorter and 

 the fourth relatively much longer and more acutely and gradu- 

 ally pointed than in Xantholinus, and this character, in con- 

 junction with the different form of the gular sutures, as stated 

 in the table, seems to prove that Gyrohypnus should not be 

 regarded as a subgenus of Xantholinus. The species are 

 smaller and more slender as a rule than in that genus, and the 

 head is less developed, but, in a similar manner, Gyrohypnus 

 is made up of a number of groups distinguished by pecu- 

 liarities of pronotal sculpture and general facies, one or two 

 of which approach some of the more aberrant groups of 

 J^an</^o?^?^?^s rather closely in appearance; this remark applies 

 particularly to our obsidianus group , which strikingly recalls 

 the American incipennis group of that genus, especially in 

 the sculpture of the head and pronotum. In geographical 

 distribution Gyrohypnus differs greatly from Xantholinus, 

 the former being poorly represented in palaearctic regions but 

 remarkably developed in the nearctic provinces, the reverse 

 being the case in Xantholinus. Our species can be readily 

 assigned to the following four subgeneric groups, defined 

 principally by pronotal sculpture : — 



Frontal grooves very long and conspicuous ; gular sutures distinct 2 



Frontal grooves short ; gular sutures effaced 5 



2 — Sides of the head vpith a broad, parallel-sided, flattened and punctured 



line, involving the lower part of the eyes and extending to the arcuation 



of the basal angles. Nearctic regions throughout % 



Sides of the head almost evenly convex, the flattened area obsolescent ; 

 surface more convex throughout, generally very feebly sculptured 4 



3 — Pronotal punctures coarse, 4-6 in number in the dorsal series... Group I 

 Pronotal sculpture finer as a rule, the punctures much more close-set in the 



dorsal series and 7-14 in number Group II 



4 — Punctures of the head and pronotum very sparse, those of the dorsal 

 thoracic series 10-12 in number; surface always highly polished and 

 devoid of minute strigilation anteriorly. Nearctic Atlantic regions. 



Group III 



5 — Dorsal series of the pronotum composed of 10-12 punctures; under 



surface of the head without minute strigilation. Sonoran regions of 



the Pacific coast Group IV 



