Diagnosis. Shell ca. 1.75 mm in height, transparent, elongate-pupiform with an entire, elliptical-oblique, moderately thickened peristome, including a small, deeply set parietal denticle and a slight columellar-basal callus.
Description
Shell minute, elongate-pupiform, pellucid when fresh, opaque shiny when older. Aperture elliptical-oblique, somewhat higher than wide, taking up less than one third the shell height, outer lip moderately reflected, thin above, increasingly thickened on its outermost extension by a heavy deposit of callus upon its surface and inner edge; columellar margin has a callus and an acute entering fold above. Whorls convex, moderately rounded, ranging from 4.8-5.4 in number. Suture deep. Protoconch bulbous. Teleoconch sculpture consists of weak, irregular oblique striae. Maximum width of body whorl extends 1/6 beyond the rim of the peristome in side view facing left. Palatal rim appears alabaster-like. In profile view facing left, the peristome of the mature shell gently curves in at the upper edge, expands moderately and then bends gently back at the base of the shell in alignment with the central axis. A small, deeply set, parietal denticle is almost centrally positioned on the parietal face. The tiny, deeply set parietal denticle is partially visible in umbilical view. Internally, from the dorsal and aperture-facing-right perspectives, the columella bears a single, simple elongate lamella beginning one third the distance from the top of the penultimate whorl, which elaborates into a characteristic, broadly winged, tongue-like structure in aperture-facing-left position. In ventral perspective, the lamella is slightly sinuate, whereby the first thickened flexure directed upward is in alignment with the columellar axis. The lamella culminates at the base of the gently twisted columella as a small, deeply set, well-formed, non-sinuous denticle. The base of the columella spindle (portion under the tongue-like lamella) is moderately long and dilated by the final manifestation of the columellar lamella forming the parietal denticle.

Differs from Carychium floridanum G.H. Clapp, 1918 by the more bulbous protoconch, the thinner, less rounded and less swollen peristome, the enhanced elaboration of sinuosity and thickness of the columellar lamella (interior ventral view) and the downward projection of the lamella in tonguelike form, the presence of the parietal denticle in umbilical view and the reduced size of the deeplyset parietal denticle; from C. mexicanum (RBINS 10591.2, "Texolo Falls, V. Cruz [Veracruz], Mexico" (Pilsbry 1948) by its larger and more tapered shell, the thinner, less swollen peristome, the first flexure of the sinuate lamella synchronal with the shell axis as seen in the interior ventral view, the more elaborate configuration of the columellar lamella (in side view-left perspective) and the tininess of the parietal denticle; in C. costaricanum (RBINS 10591.1), "San Jose Plateau Costa Rica" (von Martens 1898), the shell is more robust with increased roundness of the whorls, the aperture is markedly more auriform, the peristome is greatly thickened (swollen) and rounder with a thick columellar-basal callus in the inner left-hand corner, the columellar lamella is simple and smooth without wing-like elaboration, the parietal denticle is thick and less finely defined as in C. hardiei.

Distribution. This species is only known from the type locality at Indian Springs State Park, ca. 90 km south of Atlanta, Georgia. The drainage basin where these individuals were collected was located proximate to the park entrance and adjacent to the latrine complex (Fig. 10). It remains questionable whether any of the socalled C. mexicanum distributions included in Hubricht (1985) for the southeastern United States include C. hardiei sp. n. Moreover, Hubricht (1985) explicitly states that faunistic surveys were largely lacking in the State of Georgia and thus, the existence of C. hardiei sp. n. could well have been overlooked completely.
Ecology. Mixed deciduous leaf litter.
Conservation. In the drainage basin where this species was found (see above), live individuals occurred in relative abundance, suggesting that C. hardiei has optimum ecological conditions to survive there. Still, on a global scale, its current distribution may be limited to the 2.14 square kilometres of woodland in the middle of Georgia, regarded as Indian Springs since 1825 and as a "State Forest Park" since 1927. In conjunction with the Guidelines for the IUCN Red List (IUCN Standards and petitions Subcommittee 2014) it likely constitutes a Critically Endangered narrow range endemic (CR Bl). Habitat disturbance by pollution and human encroachment via tourism or urban development may pose the greatest threat.