Calistocoris Reuter, 1881

(Figs. 4, 5)

Calistocoris Reuter, 1881: 318 . Type species: Calistocoris caesareus Reuter, 1881; by monotypy.

Polychitonocoris Miller, 1940: 597 . Type species: Polychitonocoris formosus Miller, 1940; by original designation. Synonymized by Coscarón, 2002: 27.

Reuter (1881) described the monotypic genus Calistocoris with a single species, C. caesareus, from Borneo. Fiftynine years later, Miller (1940) described the new genus Polychitonocoris for two new Malaysian species: Polychitonocoris formosus Miller, 1940 from Sarawak and Polychitonocoris virgo Miller, 1940 from Pahang. All three species remained unmentioned in the literature, other than in the two global catalogs (Putshkov & Putshkov 1985, 1987; Maldonado Capriles 1990), until Coscarón (2002) redescribed the taxa, correctly synonymizing P. formosus with C. caesareus .

As Coscarón (2002) did not include much comparative justification, I offer my own independent observations: It is unsurprising that Miller (1940) did not make any comparisons in his original description between Polychitonocoris and any other peiratine genus, as the slender form of the head and pronotum is unique among peiratine assassin bugs. However, Calistocoris also possesses this feature, as was indicated in Reuter’s (1881) description: “[Pronotum] lobo antico angustulo, antice convexo”. Other morphological details shared by these two taxa are summarized in Table 1; each character state individually is not unique to the taxa, but when grouped, they all strengthen the case for conspecificity. Biogeographical evidence further supports this synonymy. Reuter’s species was described from “Borneo (Matang)”, and Miller’s type species was described from “ Sarawak, Mt. Matang”, with a paratype from Mt. Selinguid. Thus, it appears that Miller’s type species, P. formosus, is geographically syntopic with C. caesareus . The second of Miller’s species, P. virgo, comes from “ Pahang, F.M.S., Kuala Teku”. The distributional details are summarized in Fig. 6 (but see note under Materials & Methods: Biogeography). The obvious similarities and biogeographical proximity with Calistocoris would have required comparison with Polychitonocoris; thus, I have speculated that Miller must have been unaware of Reuter’s genus, despite it being present in an important and unobscure treatise on Old World Reduviidae .

When originally confirming my suspicion that P. formosus was a junior synonym of C. caesareus, I requested photographs of the male holotype of Polychitonocoris formosus (Fig. 4) and the female holotype of Polychitonocoris virgo (Fig. 5). I also requested images of the female holotype of Calistocoris caesareus from HNHM, although I have been informed that the type was borrowed 22 years ago, and despite multiple requests, has not yet been returned (Rédei, pers. comm. 2017). Similarly, the female paratype of Polychitonocoris formosus purportedly deposited in SMSM is neither in that institution (Leh, pers. comm. 2017) nor in BMNH (Webb, pers. comm. 2017). Thus, the type of C. caesareus remains inaccessible, and I am unable to corroborate the synonymy as rigorously as is preferable. Nevertheless, the details discussed above strengthen the case, leaving the synonymy satisfactory until the holotype can once again be examined.

The following key will enable separation of the species: