Moved from californicus group.

Moved from Ripiphorus.

In the existing keys, the hind tarsi provide the main characters for initially separating the genus in two chunks. If the first tarsus of the hind leg is obliquely truncate at base (e.g. as in R. rex) you go one way...if it isn't, you go to the californicus group or the (more subtle, larger, and not well-settled) fasciatus group. See Plate IV at the end of Rivnay(1) for a number of illustrations of the hind tarsi of the two types.

From what I can see in the two images here, it seems this male's hind tarsi are not obliquely truncate. (You might try to verify that if you have access to the specimen.) That...together with the entirely dark abdomen...leads to the fasciatus species group in the Rivney's key. (There are no members of the fasciatus group in the key of Linsley & MacSwain(2) for CA.)

My attempt to walk the images here through the key in Rivnay(1) for the "fasciatus group" led me to R. tuberculatus (via couplet sequence 1, 2, 3, 4a...i.e. from wings hyaline with a smoky band; and elytra entirely yellow vs. yellow with dark brown base). But Champion's original description of R. tuberculatus indicates the male abdomen is reddish-yellow (perhaps with a black medial dorsal stripe and the apical segments somewhat darker). It should be noted that, at this time, the whole genus (especially the fasciatus group) is rife with ambiguity with regard to variability and possible synonymies (let alone the possibility of new undescribed taxa). So unfortunately, the situation with the male here is currently beyond my ken.