Two new species of Dicharax Kobelt & Möllendorff, 1900 from Myanmar and one from Thailand (Gastropoda: Caenogastropoda: Alycaeidae)

In this paper, three new species of the alycaeid genus Dicharax Kobelt & Möllendorff, 1900 are described, namely Dicharax ﬂ oridus n. sp., Dicharax spatiosus n. sp. (Both from Shan State, Myanmar) and Dicharax kosztarabi n. sp. (from Thailand). All three new species are known from their holotypes.

Diagnosis: A small Dicharax species with a depressed shell (shell shape low conical), regularly, sparsely spaced R1, a nearly half whorl long R2þR3, a prominent R2 swelling, a fringed aperture and a strongly expanded outer peristome.
Description: Single shell corroded, off-white, original colour unknown; shell outline slightly ovate in dorsal view; spire only slightly elevated, dorsal side low conical; body whorl rounded; protoconch moderately elevated, rather glossy, ca.1.5 whorls (although teleoconch-protoconch boundary not clearly visible); R1 of ca.1.75 whorls; first 0.75 whorls with weak wrinkles, this abruptly changes to a strongly, sparsely ribbed surface; last half R1 whorl with ca. 30 ribs, spaces between ribs much wider than a rib; ribs strong, elevated, slightly turned backwards (towards protoconch), while at the end of R1 ribs slightly turn towards aperture; boundary between R1 and R2 distinct due to denser R2 ribs, and because the rib morphology changes (i.e.R2 ribs bent towards aperture); R2 with ca.32 elevated ribs that turn towards aperture, space between ribs narrower than a rib; R2þR3 less than a half whorl (ca.1608); R2 slightly quadrangular in cross section, i.e. bears a slight keel on its middle and on its ventral side; R2 slightly shorter than R3; boundary between R2 and R3 conspicuous due to strong, elevated ribs at the beginning of R3 and a deep constriction; R3 with a prominent, elevated, but blunt swelling that is situated closer to the peristome, both sides equally steep; aperture oval, oblique to the shell axis; boundary between inner and outer peristomes conspicuous; inner peristome fringed, 6 notches result in 5 incisions, basal one most conspicuous (widest); outer peristome strongly expanded (most strongly towards dorsal and upper palatal side) and even reflected towards umbilicus; umbilicus elongate, showing all whorls, moderately wide, less than one third of shell width.

Differential diagnosis:
The combination of the fringed inner peristome, the strongly expanded outer peristome, and the sparsely ribbed R1 distinguishes this new species from all congeners.Several Dicharax species from Myanmar possesses a fringed inner peristome.Among them, Dicharax blanfordi (Godwin-Austen, 1914) (material examined: Chwegalé, Arakan Hills, NHMUK 1906.4.4.177 holotype, see Fig. 2) is the most similar to D. floridus n. sp.due to the similar ratios of shell regions and similar density of ribs.However, D. blanfordi is much larger, the inner peristome is less fringed, and the outer peristome is less expanded.Dicharax cucullatus (Theobald, 1870) is larger, it has a more depressed spire, a shorter R3 with a narrower swelling, a much less prominent outer peristome, and denser R1 and R2 ribs, and the same is true for D. davisi (Godwin-Austen, 1914) (see Jirapatrasilp et al., 2021) and D. ochraceus (Godwin-Austen, 1893) (material examined: Ruby mine Disr., Up.Burma, leg.Doherty, NHMUK 1903.7.1.2684,2 syntypes, Fig. 3).Dicharax ataranensis (Godwin-Austen, 1914) has a nearly smooth R1 (widely-spaced ribs are only visible near the suture), a shorter R2 with denser ribs, and the outer peristome is not reflected as much as in this new species.
Etymology: The specific epithet floridus (blooming in Latin) refers to the flower-like aperture.
Distribution: This new species is known from the type locality only (see Fig. 4).
Diagnosis: A Dicharax species with a depressed shell, rounded body whorl and aperture, very long R2 having bent ribs, and two prominent swellings on R3.
Description: Single shell corroded, off-white, original colour may be light brownish or pinkish; shell outline slightly ovate in dorsal view; spire only slightly elevated; body whorl rounded; protoconch low, rather glossy, ca.1.25 whorls (although teleoconch-protoconch boundary not clearly visible); R1 of ca.1.75 whorls; first whorl of R1 with dense, very fine ribs, which gradually become stronger, but remains dense until the very end of R1, which abruptly turns to more widely-spaced until end of R1; last half R1 whorl (counting until beginning of sutural tube) with ca.60 ribs; spaces between R1 ribs approximately as wide as a rib except for the end of R1, where spaces are wider than a rib; ribs low, wrinkle-like; boundary between R1 and R2 distinct due to denser R2 ribs, and higher R2 ribs; R2 with ca.58 elevated ribs that turn towards aperture; R2þR3 more than a half whorl (ca.1908); R2 inflated (i.e. its diameter is wider than that of the neighbouring R1), slightly shorter than R3; boundary between R2 and R3 conspicuous due to strong, elevated ribs at the beginning of R3 beginning and a deep constriction; R3 with a prominent, elevated and sharp central swelling bearing some ribs, and an additional swelling between the main swelling and the peristome; second swelling starts from the Photo: Kevin Webb, NHM suture, but disappears before umbilicus (most visible in lateral view); aperture oblique to shell axis, rounded, not fringed; boundary between inner and outer peristomes conspicuous; inner peristome prominent, expanded and even reflected towards umbilicus; outer peristome wider, strongly expanded in one plane, reflected only towards umbilicus; umbilicus shows all whorls, moderately wide, less than one third of shell width.
Operculum: The operculum of the holotype was in its aperture.Operculum concave, outer side with remains of a very slightly elevated lamina; nucleus missing, there was probably an elevated central nipple on the inner side.
Measurements: SW 5 5.01 mm, SH 5 3.06 mm., 1914) is smaller, has a blunter R3 swelling, lacks a second R3 swelling, and has a shorter R2 (see Páll-Gergely et al., 2021).D. cucullatus is similar to this new species in size and the long R2, but its R3 swelling is situated closer to the peristome, lacks a second R2 swelling, and has a fringed aperture (see Jirapatrasilp et al., 2021).Dicharax woodthorpei (Godwin-Austen, 1914) (see Páll-Gergely et al., 2021) is also somewhat similar to the new species in terms of general shell and aperture shape, but it lacks a conspicuous second R3 swelling, and its R2 bears no elevated ribs, but has light and dark alternating colour stripes (or some of the R2 ribs may be separated individually at the beginning of R2).
Etymology: The specific epithet spatiosus (spacious, wide in Latin) refers to the wide aperture and spacious R3 of this new species.
Distribution: This new species is known from the type locality only (see Fig. 4).

Remarks:
The holotype has a scraped hole on its R2, suggesting that it was probably eaten by an Atopos slug (Fig. 5).
Additional material: 6 juvenile/broken shells (not paratypes), coll.HA, same data as for the holotype.
Diagnosis: A Dicharax species with a depressed shell, pinkish colouration, regular, rather widely-spaced ribs on the last whorl of R1, a short R2 with dense, bent ribs, and a rounded aperture.Description: Shell off-white to pinkish/light brownish; shell outline slightly ovate in dorsal view; spire only slightly elevated; body whorl rounded; protoconch low, rather glossy, ca.1.25 whorls; R1 of 1.75 whorls; first whorl of R1 with dense, fine ribs (spaces between ribs only slightly wider than a rib), which gradually become more widely-spaced (spaces between ribs at the end of R1 are much wider than a rib); last half R1 whorl with ca.32 ribs; ribs straight, strong, narrow, but relatively low; boundary between R1 and R2 distinct due to much denser R2 ribs; R2 with ca. 30 low and rather narrow ribs, spaces between ribs is approximately as wide as a rib; R2þR3 more than a quarter whorl (ca.1108); R2 shorter than R3; boundary between R2 and R3 conspicuous due to smooth R3 and a deep constriction; R3 nearly smooth, glossy, only with weak growth lines, and blunt but prominent, elongated central swelling; aperture oblique to shell axis, rounded; boundary between inner and outer peristomes distinct; inner peristome prominent, slightly protruding; outer peristome as strong as inner peristome, strongly Operculum: unknown.Measurements: SW 5 2.7 mm, SH 5 1.7 mm.Differential diagnosis: Dicharax subroseus Páll-Gergely, 2021, which is the most similar species, has more widely-spaced, stronger R1 ribs, deeper constriction between R1 and R2, more sparsely spaced ribs on R2, and a more expanded inner peristome (Páll-Gergely et al., 2021).Dicharax panhai Jirapatrasilp & Páll-Gergely, 2021 has a more conical dorsal side, an oval umbilicus, a shorter combined R2þR3, less (18) ribs on R2, its R3 more prominent ribs, and the swelling is situated closer to the peristome.
Distribution: This new species is known from the type locality only (see Fig. 4).
Remarks: The type locality of D. kosztarabi n. sp. is situated only 7-8 km from the type locality of D. panhai.This also highlights the local endemism and high species diversity of this group in the Thai-Myanmar border region.