Genus Alycaeus Gray, 1850

Alycaeus Gray, 1850: 27.

Orthalycaeus L. Pfeiffer, 1876: 57 (partim).

Alycaeus (Alycaeus) - Thiele 1929: 108; Wenz 1938: 478; Egorov 2013: 33.

Type species.

Cyclostoma gibbum Eydoux, 1838 (= Alycaeus eydouxi Venmans, 1956)

(Fig. 6A), SD Nevill (1878: 290). Cyclostoma gibbum Eydoux, 1838, is a junior homonym of Cyclostoma gibbum Draparnaud, 1805. Thus, Venmans (1856) proposed Alycaeus eydouxi Venmans, 1956 as a replacement name.

Gray (1850) originally included two species within Alycaeus ( A. gibbus Eydoux, 1838 and A. strangulatus L. Pfeiffer, 1846) without selecting either of them to be the type species.

Diagnosis.

Shell very large (D: 8-15 mm), triangular, with body whorl being dominant due to very long R2; protoconch smooth, obliquely striated, or transitional character state of the two; R1 usually finely reticulated, due to fine radial ribs and fine spiral striation; R2 long or very long (usually almost reaching 0.5 whorl), smooth or with lamella-like, straight, dense ribs; umbilicus narrow. Operculum thin or relatively thickened (can have both calcareous and proteinaceous layers, Foon and Liew 2017), without elevated outer structure (although scaffold-like calcareous structure and appressed radially spiral lamellae can be present, see Foon and Liew 2017). Central tooth with five cusps, broad, central cusp blunt.

Differential diagnosis.

The sculpture of Alycaeus and Chamalycaeus (smooth protoconch, spirally striated, weakly ribbed teleoconch) are identical, although Chamalycaeus tend to have stronger ribs. The distinction is based on the narrow ( Alycaeus ) and wide ( Chamalycaeus ) umbilicus. Furthermore, Alycaeus shells are larger, more colourful (reddish or yellowish) and the very long (i.e., ca. 0.5 whorl-long) R2 in Chamalycaeus is very rare.

Typical Pincerna has a relatively short tube and a strongly ribbed teleoconch, whereas typical Alycaeus possesses a long tube and its teleoconch is weakly ribbed. Some species ( P. anceyi , P. mouhoti ) form connections between the two genera. However, we prefer to maintain the distinction between Pincerna and Alycaeus due to the many species characteristic to both respective genera.

Alycaeus is easily distinguished differs from Stomacosmethis which has a yellowish-orange, triangular shell, and a very short tube.

Distribution.

This genus is known from northern Laos and northern Vietnam until the southern end of the Malay Peninsula (Fig. 7).

Remarks.

Regarding the authorsip of Alycaeus (i.e., Baird vs. Gray), we follow Petit (2012: 24-25).