Individuals of this species are best told by the very transverse pronotum, maximum pronotal width/median pronotal length of 1.39–1.42 in association with the very broad pronotal base and broadly based, subparallel elytra (Fig. 10C). Along with individuals of Meonochilus eplicatus, the elytral striae are not so deep, and thus the elytral intervals are correspondingly less convex. However, as in individuals of Meonochilus spiculatus and Meonochilus rectus, the elytral intervals are glossy, without evident microsculpture. The male aedeagal median lobe exhibits an apex that is broadly, ventrally expanded (Fig. 16C, 16D), and a membranous internal sac with a spiculate basal lobe on the right side (Fig. 16C, 16E). Standardized body length 5.7–6.1 mm.

(n = 4). Aedeagal median lobe with deep sagittal crest, shaft broad and robust, ventral margin straight before very broadly rounded and downturned apex; internal sac densely covered with microspicules, the spicules on a rounded, ventroapical lobe somewhat larger; ventral right paramere elongate, length equal to 0.75× the distance from point of parameral articulation to external face of apex, sides parallel and apex subtruncate, apical half of ventral surfaced lined with 7–18 long setae, only 1 subapical seta on truncate apex, and 0–1 small setae near apex on dorsal edge; dorsal left paramere broad, elongate, length equal to 0.8× distance from parameral articulation to outer apical face, ventral margin recurved and dorsal margin straight resulting in a “wooden shoe-like” shape, apex (i.e. toe) bluntly rounded, 3–4 setae on ventral surface of apex.

(n = 1) Bursa copulatrix exceedingly elongate, distance from gonocoxal bases to bursal apex 3.2× maximal bursal breadth, the membranous bursal surface thin throughout based on minimal staining with Chlorazol Black; spermatheca present as broad, bulbous wart-like structure situated subapically on left surface of bursa (Fig. 17C); spermathecal gland duct entering spermatheca via elongate, expanded base; common oviduct joined to bursa immediately distad gonocoxal bases; basal gonocoxite 1 with lateroapical series of 2 setae, 1 larger, 1 smaller, and mesal series of 5–6 setae along apical half of mesal surface (Fig. 17D); gonocoxite 2 broadly spatulate apically, with 2 acuminate lateral ensiform setae and 1 dorsal ensiform seta along dorsomedial margin; apical sensory furrow bearing 2 nematiform setae near midlength of gonocoxite 2, the nematiform setal insertions at 0.55× gonocoxite length.

Lectotype male (BMNH), mounted on plain white platen, labeled: Manaia // var. / 61 // New Zealand / Broun Coll. / Brit. Mus. / 1922 – 482. // Lectotype ♂ / Tropopterus / placens / Broun, 1880 / det. J.K. Liebherr 2011 (black-bordered red label) // Meonochilus / placens ♂ (Broun) photo / det. J.K. Liebherr 2010. Paralectotype female (BMNH), mounted and labeled as lectotype, except for: 61. [blue label] // Type (round red-bordered label) // ... // Paralectotype ♀ [sixth label].

ND: Bream Head, Whangarei, 35°50.68'S, 174°34.85'E, 01-vi-1957, Watt(?) (NZAC, 1), under stone, 310 m el., 08-vii-1957, Watt (NZAC, 1); Mt. Manaia, Whangarei Heads, 35°49.11'S, 174°31.02'E, 14-iii-1970, May (NZAC, 1).

Though this species was first collected by Thomas Broun, and subsequently collected by Charles Watt, it has never been found anywhere except in the Whangerei Heads area north of Whangarei Harbor, Northland (Fig. 15). The restricted distribution of this species reiterates Watt’s (1977) concerns about the importance of conserving type localities of New Zealand insects in order to maintain biodiversity. The sister group relationsip between Meonochilus placens and the more widespread western Northland Meonochilus eplicatus, suggests that Whangarei Heads has been a peripherally isolated locality at which the population of Meonochilus placens speciated from populations comprising the geographically more widespread and morphologically more variable Meonochilus eplicatus. In this instance, then, Whangarei Heads is both a center of speciation and a presently limited biodiversity hotpot.

The lone ecological note for the five known Meonochilus placens specimens involves collection of one under a stone; thus this is apparently a terrestrially bound species.