There are in the Leyden Museum two specimens of an Amphidromus, that I was not able to identify with any species represented in our collection. In my opinion they had characters of both A. porcellanus Mouss. and A. sumatranus Marts., and also of A. adamsi Rve, which latter species has notoriously numerous forms. To be quite sure I asked the advice of Mr. Hugh C. Fulton, who had the kindness of comparing the Leyden Museum specimens with specimens in his own collection. Mr. Fulton wrote to me that the larger specimen agrees with specimens of his own, which lie decided were a variety of A. semifrenatus Marts., while he possessed also specimens as carinate as the smaller one, which may possibly belong also to this species. Thinking it might be of some interest to conchologists, the more so while there are not existing in literature, as far as I know, figures of A. semifrenatus, I am giving here figures of both specimens. The larger one (figs. 1 en 2), Leyden Museum Amphidromus 57a, is collected at Tapatoean, Atjeh, northwestcoast of Sumatra, and presented to the Museum by Mr. H. E. Wempe. The shell is greyish brown, darkest on the latter half of the last whorl. A small dark chestnut zone surrounds the closed umbilicus. The last whorl and the latter half of the penultimate whorl are encircled by a small peripheral band, composed of alternating white and chestnut blots, resembling that existing in A. sumatranus. The former half of the penultimate whorl and the preceding one are wholly covered with irregular alternating, larger white and narrower chestnut stripes; in the middle is to be seen very indistinctly a small band in the groundcolour of the shell.