According to Pilsbry, the only Gastrocopta without palatal folds is G. corticaria , but he gives its height as 2.5 mm. Assuming that the height distribution of the G. armifera shells is normal, we can calculate the probability that a 4.97-mm long shell may be a member of the G. armifera population. The mean height and the standard deviation of 30 adult G. armifera shells from the same location were 4.33 mm and 0.126 mm, respectively. Therefore, based on this analysis, we can safely conclude that the Gastrocopta shell in question is not a member of the G. armifera population at the location where I found them. A G. armifera shell from the same location.
Scale is in millimeters.
Don t hesitate to send to me your bright ideas about the identity of this shell.