184 AMPHIDROMUS. 



above, rose colored inside. Columella a little twisted, brighter rose 

 tinted ; peristome reflexed, roseate, the ends joined by a rose-tinted 

 eallus. Length 52, diam. 25. aperture 24 mill. (Bavay}. 



Rhone, on the upper Mekong river (Massie). 



A. laosianus BAVAY, Journ. de Conchyl. xlvi, 1898, p. 15, pi. 2. f. 

 1, 1 a; with var. albo-ccerulescens , p. 16, pi. 2, f. 2, 2 a. 



The pink aperture and peristome give individuality to this species. 

 There is a single black-brown varix on the last or penultimate whorl, 

 and in this it differs from the species with which I have provisionally 

 associated it. 



Color-var. alboccerulescens Bavay. PL 62, figs. 62, 63. 



Bluish- white, with paler streaks representing the brown ones of 

 the typically colored form. Aperture roseate, but paler. One or 

 two black varix-bands on the last whorl. Occurred with typical 

 laosianus. 



II. SINISTRAL DIVISION (Section Syndromus). 



Shell always sinistral, usually thin, and never marked with varix- 

 stripes; the parietal callus usually thin and transparent. The 

 epiphallus and flagellum are much shorter than in typical Amphi- 

 dromus. 



Species of this division extend along the island-chain from Java 

 east to the Tenimber Islands, in Celebes, Borneo and the adjacent 

 extreme of Paragua, Sumatra, and on the continent northward to the 

 Sylhet Hills and the southern border of China. The species are 

 excessively variable, and some forms from continental Asia are sin- 

 gularly like species of Java and even Timor. The xiengensis and 

 porcellanus groups are thus merely continental and insular forms of 

 the same type. 



The species are if possible more arbitrary than among the large 

 forms of the genus. The following key to groups is quite artificial. 



Groups of Southeastern Asia (mainland}, 

 a. Shell longitudinally ribbed, thin, the peristome brown. 



Group of A. begmi, p. 188. 

 a 1 . Not ribbed. 



b. Peristome colored ; shell yellow or with green lines. 



Group of A. mouhoti, p. 185. 



b l . Peristome white ; shell yellow or with two bands at base ; 

 columella with a shallow groove at its insertion. 



Group of A. sylheticus, p. 188. 



