P. heroicus or californicus??

Greetings,

From what I can see, I would agree that it is a female of Prionus heroicus. The pronotum is nearly as broad as the base of the elytra in P. heroicus, while in P. californicus, the pronotum is narrower than the elytral base. Your specimen clearly exhibits the very broad pronotum characteristic of P. heroicus.

A couple other characters you can check are whether the metasternum is pubescent or nearly glabrous. In P. heroicus, it is nearly glabrous, and in P. californicus it is pubescent. Also, the intercoxal process of the abdomen is somewhat enlarged in P. heroicus, and narrow in P. californicus. If you need help with these characters, post a closeup of the underside, showing the region from the middle of the abdomen to the base of the front legs.

Finally, P. heroicus tends to be more blackish, like your specimen, while P. californicus is typically more reddish-brown.

I have no female of P. heroicus in my collection, despite having several males. If you have an interest in exchanging this specimen, let me know

Cheers!
Bandrow

To show the above points here is a photo of the underside of Prionus heroicus (Geoffroy, 1762) on the left and Prionus californicus (Motschulsky, 1845) on the right. Thanks for your help!
--Royce