FRANK E. BLAISDELL, SR. 331 



The more detailed differences are: 



Head coarsely and densely punctate behind with a mixture of large and small 



punctures, sparse medially before the suture (arenarius); nearly as in arenari- 



riiis but very coarsely, densely punctate behind the suture (sternalis). 



Entire basal region of head impunctate (arenarius) ; ? {sternaUs). 

 Epistoma moderately convex medially, flat laterally (arenariu.s) ; medially 



tumescent, rugosely but less densely punctate, flattened apical lobes more 



finely, closely and densely punctate (sternalis). 

 Pronotum two and a half times as wide as long, sides strongly converging from 



base to apex and broadly arcuate, gradually more rounded basally, apical 



angles very evidently rounded (arenarms); less abbreviated, sides less 



strongly converging, broadly and subevenly arcuate from base to apex, 



apical angles more distinct and less rounded (sternalis). 

 Pronotal surface sparsely and very strongly tjut not very coarsely punctured, 



punctures closer and laterally mingled with some that are much coarser 



(arenarius); surface similarly but sparsely punctate, the larger lateral 



punctures less coarse (sternalis). 

 Pronotal sides not very widely declivo-explanate, bead strong (arenarius); 



sides more broadly dechvo-explanate, bead similar (sternalis). 

 Abdomen finely but strongly, sparsely punctate, more coarsely, densely so on 



last segment (arenarius) ; almost similarly punctate, last segment relatively 



less densely so (sternalis). 

 Prosternal process only moderately constricted between the coxae (arenarius); 



process very strongly constricted, neck scarcely more than half as wide as the 



dilated and rounded posterior part (sternalis). 

 Casey has said nothing about sexual diff'erences. 



The above tabulated and comparative notes give the salient 

 synoptic and descriptive characters between the six forms of 

 the arenarius section, and the relative differences between 

 arenarius and sternalis, which are paralleled closely by obscurus 

 and scolo'pax, latus and amplicollis. 



Note that the differences are relativeh^ slight, that the sexual 

 differences are not considered, and that these insects are very 

 variable, as has been and can be shown in any large series taken 

 from a single sand dune anywhere between San Diego and 

 Humboldt Bay. 



The following characters arc common to arenarius (obscurus 

 and scolopax), sternalis, and latus {amplicollis): 



Epistoma broadly and very feebly siiuiate, the sinus generally subevenly 

 rounded, base arising more or less abruptly from the frontal suture. 



Front of the head more or less strongly, broadly and transversely impressed 

 behind the suture. 



TRANS. AM. ENT. SOC, XLV. 



