204 GEO. H. HORN, M. D. 



This species exhibits very nearly as much variation as pennsylva- 

 iiica, while preserving a facies which enables it to be quite readily 

 recognized. 



In the normal form the live spots on the thorax are well marked, 

 and the metasternum entirely or in great part piceous. The spots 

 may become obliterated until only the two anterior ones remain. 



Specimens from near Fort Yuma have the underside entirely yel- 

 low, while the thoracic spots may be well developed. These have 

 been described as pura Lee. 



Rarely individuals occur with the median elytral vitta entirely 

 wanting, still more rarely the submarginal vitta is wanting. 



The median vitta is usually very narrow, but specimens from Mis- 

 souri in my cabinet have all the vitta a little wider, so that the yellow 

 space on either side of the median vitta is not wider than the vitta. 



The oblong form of this species makes it intermediate between the 

 pai-allel form o? pennsylvanica and the more truly oval form of those 

 which follow. 



From the two species which follow, having the abdomen densely 

 punctured, it may be known by the coarsely punctured vertex ; 

 caroliniana has a {)ale head and lal)ruin, crenlcollU has a more oval 

 form, wider vittte and the sutural and marginal unite at apex. 



This insect has long borne the name alternatn in our cabinets 

 through an erroneixis interpretation of Illiger. It cannot be alter- 

 nata because that species is described from Carolina and Pennsyl- 

 vania, and it is quite unlikely that Illiger could have had specimens 

 of an essentially western species in his hands in 1807. Moi-eover, 

 Illiger describes alternata as having a pale head. It is more than 

 probable that alternata is a synonym of caroliniana, as will be seen 

 by reference to remarks under that species. 



From the fact that the name given by Say is now disposable I 

 have used it in preference to any of the names which have been 

 given in more recent times. 



The present species is especially that of the entire region west of 

 the Mississippi River, extending from our northern boundary to 

 Mexico and from the Mississipj)! to the Pacific. Single specimens 

 are in my cabinet from Illinois, Virginia and Massachusetts. 



3. D. creiiicollis Say.— Oval, slightly narrower in front. Autennge half 

 the length of the body, black, the three basal joints pale on the under and pos 

 terior side. Head either entirely yellow or with the occiput piceous, frontal 

 carina very obtuse, the tubercles feeble or absent, surface smooth, a feebly pnnc- 



