616 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 117 



An annotated catalogue of Amphidromus (Laidlaw and Solem, 

 1961) was completed before this study was undertaken, and, for the 

 sake of brevity, literature references are restricted to the original 

 citations and the discussion in the recent catalog. 



The laborious calculation of standard deviations was performed by 

 Mr. Ernest J. Roscoe. 



Cited localities. — Variant spellings of Thailand city and place 

 names are numerous, requiring great care in designating localities. 

 Fortunately, a gazeteer of Smith's collecting stations and a condensed 

 itinerary of his travels has been given by Riley (1938). All the local- 

 ities mentioned below can be located through use of this paper. 



Distribution in Thailand. — Nine species were recognized in the 

 available material. Accepting the zoogeographic division into South- 

 east, East, Central, North, West, and Peninsular Thailand (Riley, 

 1938), the most species are found in Peninsular and Southeast Thai- 

 land, seven and six respectively; the fewest in West and North Thai- 

 land, one and two respectively. The larger, "typical" Amphidromus — 

 A. inversus annamiticus and A. atricallosus — are concentrated in 

 Southeast and Peninsular Thailand although A. atricallosus extends 

 into the nearby fringes of Central, West, and East Thailand. A. 

 areolatus, A. semitessellatus, and A. schomburgki (to a lesser extent) 

 also show the Peninsular and Southeast Thailand distribution. There 

 are single records for A. areolatus in both Central and East Thailand, 

 while A. schomburgki is apparently common in East Thailand. A. 

 xiengensis is known from North, Central, and Southeast Thailand, 

 A. sinensis indistinctus from North and (?) Peninsular Thailand, and 

 A. fultoni from a single juvenile collected in Peninsular Thailand. 

 These data are insufficient to allow other than the most general 

 statements. Obviously the number of species drops off sharply from 

 South to North, and the northern part of Thailand represents the 

 fringes of distribution for Amphidromus. In Burma, Pakistan, and 

 part of India, some Amphidromus are known from more northerly 

 latitudes than in Thailand, but the distributional picture in Laos, 

 North Viet Nam, and possibly Southern China is uncertain. 



Review of species. — Laidlaw and Solem (1961) recognized 20 

 species groups in Amphidromus, divided into the subgenera Syndromus, 

 Goniodromus, and Amphidromus sensu stricto, and a "base stock" 

 series of six groups from mainland Southeast Asia that could not be 

 assigned to subgenera with any degree of assurance. They hypothe- 

 sized that Syndromus, Goniodromus, and Amphidromus represented 

 directions of differentiation that were well marked on Indonesian 

 islands but had not become clea^rly recognizable on the mainland. 

 Study of the Thailand material confirmed this impression of close 

 affinities among the mainland species, particularly in regard to 



