24 William F. Adams and Susan G. Brady 



During the spring of 1994, while performing a survey of the 

 mollusks of Town Creek, a tidal swamp stream tributary to the lower 

 Cape Fear River in adjacent Brunswick County, SGB discovered a 

 population of Helisoma eucosmium approximately 14.5 km (9 mi) 

 SSW of the type locality (Fig. 1). Although much of this stream 

 system remains to be investigated, the taxon is known to occupy at 

 least a 1.75 km (1.1 mi) stretch of the main creek. Five specimens 

 were deposited in the invertebrate research collection at the North 

 Carolina State Museum of Natural Sciences, Raleigh (NCSM). All 

 conform precisely to the original shell description given by Bartsch 

 (1908), particularly in displaying the chestnut-colored bands (Figs. 2 

 and 3). The largest specimen (NCSM #P1207), collected on 30 April 

 1994, has a greater diameter of 6.0 mm, a lesser diameter of 4.75 

 mm, and a height of 3.0 mm. It was probably an adult that overwintered, 

 a likelihood suggested by its size and the minor pitting and corrosion 

 of the shell surface. Three specimens taken in early July 1994 (NCSM 

 #P1208) are smaller; average dimensions of three specimens are maximum 

 diameter 3.8 mm, minimum diameter 3.0 mm, and height 1.9 mm 

 (n = 3). Similarly-sized specimens taken from the same period laid 

 eggs in captivity indicating that sexual maturity had been attained. 



The molluscan community in the freshwater part of Town Creek 

 is diverse; species encountered to date are listed in Table 1. Continuing 

 surveys may disclose additional species and most of those historically 

 documented (Adams 1990a) from the type locality of Helisoma eucosmium 

 may ultimately be found. 



In his description, Bartsch (1908) assigned Helisoma eucosmium 

 and a subspecies from Louisiana, H. eucosmium vaughani, to the 

 genus Planorbis Miiller 1774. F. C. Baker (1931) restricted that genus 

 to species of European origin and, without examination of soft tissue 

 anatomy, provisionally placed eucosmium in the genus Helisoma Swainson 

 1840. In his subsequent monograph on the Planorbidae, Baker (1945) 

 retained this assignment, placing it alone with Helisoma anceps (Menke, 

 1830) in the subgenus Helisoma s.s.; however, he made no reference 

 to anatomical examinations supporting this placement. On the strength 

 of unpublished observations by J. P. E. Morrison of live individuals 

 of H. e. vaughani from Louisiana, Fuller (1977) tentatively assigned 

 the species to the Central American genus Taphius H. & A. Adams 

 1855. Taphius and other planorbid genera of tropical affinity (Afroplanorbis 

 Thiele 1931, Biomphalaria Preston 1910, Australorbis Pilsbry 1934, 

 Tropicorbis Pilsbry and Brown 1914, Planorbina Haldeman 1842, 

 Armigerus Clessin 1884, and Platytaphius Pilsbry 1924) have long 

 been the subjects of taxonomic debate and divergent systematic treatment, 



