Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea) Author Páll-Gergely, Barna Author Hunyadi, András 0000-0003-3488-2817 hunand@freemail.hu Author Grego, Jozef 0000-0002-4977-0415 jozef.grego@gmail.com Author Reischütz, Alexander 0000-0002-8844-7004 alexander.reischuetz@gmx.at Author Auffenberg, Kurt 0000-0001-9660-6776 kurtauffenberg@gmail.com text Zootaxa 2021 2021-05-18 4973 1 1 61 journal article 6241 10.11646/zootaxa.4973.1.1 d0967b08-98d1-4ccd-b472-a678e0e57eda 1175-5326 4771958 42EB4BF2-A571-4894-9EEF-783649A27E4F Chamalycaeus irmatallus Páll-Gergely n. sp. Figs 9 , 10A Material examined. Holotype : Thailand , Surat Thani Province , limestone mtn., 6 km S of Na San , 8°39.583’N , 99°23.883’E , 100 m a.s.l. , 3 Jun. 1987 , F.G. Thompson leg., UF 279508 (D: 2.02 mm , H: 1.32 mm ) . Paratypes : 11 shells, same data as holotype, UF 551216 . Other material: 6 shells, Myanmar , Thayet-myo, Pegu , coll. Blanford , NHMUK 1906.4.4.71; 1 shell, Thailand , Phang Nga Province , Phang Nga , Tham Nam Phud , 8°27.829’N , 98°32.617’E , 40 m a.s.l. (locality code: 2015/33), 20 Feb. 2015 , A. Hunyadi leg., around the cave, HA . Etymology. The specific epithet is an anagram for armillatus , a species with which this new species has been confused (see Differential diagnosis). Diagnosis. A tiny Chamalycaeus species with glossy shell, irregularly, finely ribbed R1, very short R2 with blunt, low ribs, and somewhat longer R3 (the two latter regions are shorter than a quarter whorl combined). Description. Shell off-white, rather glossy, although available shells are somewhat eroded; shell outline slightly oval in dorsal view; spire slightly elevated, conical-domed; body whorl somewhat “parabolic” in apertural view; protoconch rather low, glossy, spiral striae lacking, 1.25 whorls; R1 of 1.5–1.75 whorls, with very indistinct, irregular, low and rounded, relatively wide ribs, and some weak spiral striation; boundary between R1 and R2 distinct due to change in intensity and strength of ribbing; R2 short, only ca. 16–20 ribs; R2+R3 less than quarter whorl (ca. 70–80˚); R3 up to twice as long as R2; boundary between R2 and R3 clear due to change in rib morphology, although constriction very shallow; R3 with very fine, rounded ribs, and low, convex, elongated central swelling; aperture round, slightly oblique to shell axis; boundary between inner and outer peristomes distinct, inner peristome strongly protruding, thickened, slightly expanded; outer peristome slightly weaker or as strong, also expanded, only slightly reflected toward umbilicus; umbilicus relatively narrow, ca. one third of shell width. Measurements. D: 1.75–2.02 mm , H: 1.15–1.32 mm . Operculum. Unknown. Differential diagnosis. Chamalycaeus armillatus ( Benson, 1856 ) (material examined: Thayet-Mio, UMZC 102995, holotype , Fig. 10B ) has a more rounded body whorl, longer R2 and R3, and a thicker peristome with greater distance between the edges of the inner and outer peristomes. Distribution. The type locality is in Thailand’s Surat Thani Province. A single shell was collected in the neighbouring Phang Nga Province (locality code: 2015/33, coll. HA). Shells collected more than 1,000 km north in Thayet, Myanmar are so similar to the Thai populations that they could not be separated (see below) ( Fig. 3 ). Remarks. Chamalycaeus armillatus was described from an eroded specimen. Some spiral striations are visible on the holotype , but they might be the part of the lower shell layer. Thus, this species was provisionally assigned to Chamalycaeus in Páll-Gergely et al. (2020) . Specimens from Thayet (NHMUK 1906.4.4.71, labelled as armillatus ) have slightly less densely arranged R2 ribs than typical C. irmatallus n. sp. A single, eroded shell from Tham Nam Phud ( Thailand ) is somewhat larger than the holotype of C. irmatallus n. sp. , and has a longer R2. Since all other shell characters are identical, we provisionally identify the Tham Nam Phud and Thayet specimens as C. cf. irmatallus n. sp.