See text Amphidromus is a genus of tropical air-breathing land snails, terrestrial pulmonate gastropod mollusks in the family Camaenidae.

Since then, the genus has been extensively studied: several comprehensive monographs and catalogs were authored by naturalists and zoologists during the time period from the early 19th to the mid 20th centuries.

Not until Eduard von Martens (1867) published his monograph[6] was there an attempt to cover the entire complex of species within this genus.

When Henry Augustus Pilsbry's 1900 monograph Manual of Conchology[8] appeared, the number of species in the genus Amphidromus had increased to 81, and these were placed in nineteen groups.

The papers of American malacologist Paul Bartsch (1917, 1918, 1919)[9][10][11] on the Philippine species, Bernhard Rensch (1932)[12] on the Lesser Sunda Islands forms, and Tera van Benthem Jutting (1950, 1959)[13][14] on Javan and Sumatran populations are especially comprehensive.

Adolf Michael Zilch (1953)[16] listed type specimens in the Senckenberg Museum, and illustrated many previously unfigured species.

However, several species recognized by Pilsbry have subsequently been subordinated to subspecific or varietal status, and a few names have been transferred to incertae sedis, since they are based on hundred-year-old references that have not been substantiated by more recent collectors.

[4] Species in the genus Amphidromus usually have smooth, glossy, brightly colored, elongate or conic, dextrally or sinistrally coiled shells.

However, a significant number of species in this genus are "amphidromine"; this term means that both left- and right-handed shell coiling are found within the same population.

The whorls of the shell of species of Amphidromus are moderately convex and, with only a few exceptions, are smooth or have a faint sculpture of growth lines.

However, a sculpture of moderately heavy oblique radial ribs has appeared at least four separate times in the genus, and can be seen in the following species: Amphidromus costifer Smith from Binh Dinh Province in Vietnam; A. begini Morlet from Cambodia; A. heccarii Tapparone-Canefri from Celebes; and the A. palaceus-A.

In A. perversus (Linnaeus) and most other thick-shelled species, the lip is internally thickened, forming a "roll" in its expansion, and has a very heavy parietal callus.

In general, many arboreal snails are brightly colored, obvious examples being the bulimulid genera Drymaeus and Liguus, the cepolid Polymita, and the camaenid Papuina.

[4] Continuous zonal patterns can take the form of whitish subsutural bands (A. similis), heavy subperipheral pigmentation (A. perversus var.

sultanus and interruptus); formation of oblique radial streaks which run parallel to (in A. inversus) or cross (in A. latestrigatus) the incremental growth lines; or almost every conceivable combination and variation of these factors.

The aperture, parietal callus, columella, lip, and umbilical region are variously marked with pink, brown, purple, white, or black.

[4] In shells of most of the species in the subgenus Amphidromus, resting stages are marked by the deposition of a brown or black radial band called a varix.

This appears to be rare in the subgenus Syndromus, although the shell of A. laevus does show evidence of interruption of the spiral banding after a resting phase.

[4] Species recognition is based on combinations of minor structural variations in the shape, aperture, whorl contour, umbilical region, and color pattern.

Adequate unselected field samples will enable a better understanding of the relative stability or variability of particular species in single localities.

Unfortunately, although it is clear that anatomical differences exist in the two species Jacobi dissected, unfortunately we do not know which forms he worked on, because he had incorrectly identified his material.

Haniel (1921)[15] dissected A. contrarius and A. reflexilabris, and Bernhard Rensch published a few scattered notes in his various faunistic surveys.

[4][8] Characters such as the long, narrow kidney with reflexed ureter and closed secondary ureter, the penial complex with distinct penis, which is continuous with the epiphallus, epiphallic caecum (a flagellum and an appendix), unbranched gametolytic duct, lack of vaginal accessory organs, and the basic condition of the nervous and retractor muscle systems support the inclusion of Amphidromus in the family Camaenidae.

[17] This group of snails occur in a wide variety of habitats in the tropics of Eastern Asia and Australasia, and is one of the most diverse families in the clade Stylommatophora.

[30] Species in the subgenus Syndromus have smaller shells (height usually less than 35 mm (1.4 in) and height/width ratio greater than 1.85), with variable color pattern.

[4][17] A third possible subgenus, Goniodromus Bülow, 1905 (type species Amphidromus büllowi Fruhstorfer, 1905),[31] is also cited in the literature, though its subgeneric status is yet to be confirmed.

[17] Molecular analyses of partial sequences of 16S rDNA of 18 distinct species carried out by Sutcharit and colleagues (2007)[18] indicate that Amphidromus is a monophyletic group.

Though the topology obtained for the subgenus Amphidromus was fairly consistent with current taxonomy, the phylogeny of sinistral Syndromus species showed no such correspondence.

[18] Despite being morphologically identical, some specimens supposedly belonging to three species, namely Amphidromus semitessellatus, A. xiengensis and A. areolatus, apparently had polyphyletic origins of mtDNA haplotypes.

Further information concerning the habits and mode of life of the species of Amphidromus is almost non-existent, however, these snails have generally been collected while they were crawling on trees or shrubs.