Ambrysus magniceps La Rivers (Figs. 17–19) Ambrysus magniceps La Rivers 1953a: Univ. Kans. Sci. Bull., 35: 1318–1319 (original description). Supplemental description. Female. Mediosternite VII (SGP) symmetrical; margins with right-angled to pointed lateral lobes slightly posterior to mid-length; posterolateral corners small, rounded; central lobe evenly rounded, slightly beyond level of posterolateral corners (Figs. 17B, 18B). Male. Accessory genitalic process of tergum VI (AGP) curved to right at approximately 20 degrees close to proximal third, angled again at approximately 80 degrees at distal third (Fig. 17C). Medial lobes of tergum VIII (pseudoparameres) symmetrical, posterolateral and posteromesal corners broadly rounded, posterior margin shallowly concave medially (Fig. 17D). Phallosoma elongate, linear, slender, tapering dorsoapically; endosoma lightly sclerotized apically on left side, digitate (Fig. 17E black arrow); endosomal sclerites knob-like, with inconspicuous denticles (Fig. 17E). Parameres symmetrical, slightly longer than maximum width, mesal margin convex. Proctiger almost as long as width at base. Pygophore with elongate setae sparsely distributed over most of surface, with thick brush of elongate setae on posterior margin (Fig. 17F). Diagnosis. This species can be distinguished from other species in the section by the symmetrical SGP with right-angled to pointed lateral lobes slightly posterior to mid-length of each margin. Additionally, the posterolateral corners are small and rounded and the central lobe is evenly rounded. The male phallosoma presents the endosoma apically sclerotized on the left side and both endosomal sclerites are knob-like with inconspicuous denticles (Fig. 17E). Comparative notes. This species has a close resemblance to A. inecol but with important differences that clearly identify them as distinct species (see Comparative notes in treatment of A. inecol). Discussion. This species measures 10.87–13.00 in length and 6.62–7.75 in width. A close relationship of this species and A. altiplanus was supported based on molecular data recently presented by Sites (2022). See Discussion section in treatment of A. inecol for the reason to refrain from reporting some specimens in various collections initially identified by DRV as belonging to A. magniceps. Variation. Some females exhibit the SGP with posterolateral corners poorly developed and inconspicuous; thus, the posterior margin is evenly rounded. Also, the central lobe can be indistinctly concave medially. Additionally, in some females the lateral lobe on the right margin of the SGP is slightly smaller, giving the plate an asymmetrical appearance. Type locality. Mexico: Estado de México: Mpio. Tejupilco, Tejupilco. Repository. Male holotype (Fig. 18A) is housed at the CAS. Published records: Mexico: Estado de México (La Rivers 1953a). New records: MEXICO: Guerrero, Michoacán, Oaxaca. Distribution. Ambrysus magniceps is distributed in central and southwestern Mexico (Fig. 19) at elevations of 600–1,300 meters. The species was previously known from only the type locality in central Mexico (Estado de México). This locality is in the Balsas Basin biogeographic province, whereas the new reports from the western part of the country are on the border between the Sierra Madre del Sur province and the southern section of the Pacific Lowlands province. Type material examined. HOLOTYPE ♂ (by original designation). MEXICO: Estado de México: [Mpio. Tejupilco], Tejupilco, Temescaltepec [District of Temascaltepec], 19-VI-[19]33 / H.E. Hinton & R.L. Usinger colls. / Ambrysus magniceps La Rivers HOLOTYPE / Ambrysus magniceps La Rivers determined by Ira La Rivers 1948 / California Academy of Sciences Type No. 10057. PARATYPES: same data as holotype but 15-VI-[19]33 / Ambrysus magniceps La Rivers ALLOTYPE / Ira La Rivers Collection bequeathed to the California Academy of Sciences - 1978 (1♀ CAS); same but Paratype Ambrysus magniceps La Rivers Det. 1978 by Vincent F. Lee / “We have the allotype in the type collection,” 06-XII-78 V.F. Lee (1♀ CAS); [Mpio. Tejupilco], Tejupilco, Temescaltepec [District of Temascaltepec], 15-VI-[19]33 / H.E. Hinton & R.L. Usinger colls. / Ambrysus magniceps La Rivers Paratype / Ira La Rivers Collection bequeathed to the California Academy of Sciences - 1978 (1♀ CAS); same but / 97 (1♂ CAS). Additional material examined. MEXICO: Guerrero: [Mpio. Chilpancingo de Los Bravo, Zoyatepec River at] Soyatepec [Zoyatepec, approx. 17º19’43.8’’N, 99º33’37.4’’W, 730 m], 25-VI-1983, M. García coll. (1♀ CNIN). Michoacán: Mpio. Chinicuila, Villa Victoria, 750 m, 10-VIII-2000, Novelo, R. coll. (1♂, 1♀ IEXA); same but arroyo en Villa Victoria, 740 m, 17-V-2002, Novelo, R. coll. (2♂, 1♀ IEXA); Mpio. Chinicuila, Villa Victoria, 700 m, 31-III-2005, Novelo, R. coll. (4♂ IEXA); same but 03-VI-2005 (1♂ IEXA); same but 10-I-2006 (1♀ IEXA); Mpio. Coalcomán, El Salitre de Maruata, 18º53’00.6’’N, 103º08’40.5’’W, 1149 m, L-1485, 25-XII-2012, Reynoso-Velasco, D. coll. (8♂, 9♀ IEXA); Mpio. Coalcomán, Río El Gauyabal at El Salitre de Maruata, 18º52’50.4’’N, 103º08’44.5’’W, 1143 m, 25-XII-2012, L-1486, Reynoso-Velasco, D. coll. (1♂, 2♀ IEXA); Mpio. Coalcomán, La Chichihua, 10-II-2005, Novelo, R & Gómez-Anaya, J. colls (1♂ IEXA); same but S[ierra] de Coalcomán, 04-VI-2005, Novelo, R. coll. (2♂, 1♀ IEXA); same but 10-VII-2005 (1♂ IEXA). Oaxaca: Mpio. Putla Villa de Guerrero, stream at Pluta de Guerrero, 17º02’21.5’’N, 97º54’42.9’’W, 767 m, 30-V-2012, L-1397, Reynoso-Velasco, D. coll. (1♂ IEXA); [Mpio. San Gabriel Mixtepec], San Gabriel Mixtepec, 20-V-1984, H. Velazco coll. (1♂ CNIN); Mpio. San Gabriel Mixtepec, km 194 carr. Puerto Escondido-Oaxaca, San Gabriel Mixtepec, Río Rana, 16º06’06.3’’N, 97º03’52.9’’W, 712 m, 27-V-2012, L-1380, Reynoso-Velasco, D. coll. (1♂, 3♀ IEXA); same but 03-IV-2015, L-1906, Reynoso, Sites, Shepard & Barr colls. (2♂, 2♀ IEXA).

Published as part of Reynoso-Velasco, Daniel & Sites, Robert W., 2025, Revision of the Ambrysus signoreti Stål species complex (Heteroptera: Naucoridae: Ambrysinae). Section 3., pp. 1-66 in Zootaxa 5735 (1) on pages 31-34, DOI: 10.11646/zootaxa.5735.1.1, http://zenodo.org/record/18020594