[1] A. watsoni measures approximately 1.7 by 1.0 mm and lacks strong defining characteristics, although some may exhibit enlarged growth lines or a black spot at the tip of the shell's spire.

In the second whorl these threads are abruptly cut off, and are replaced in the embryonic shell by about eight non-transparent spiral furrows, parted by fretted ridges.

In these interstices the surface is covered with microscopic spiral scratches, which, however, are neither sharp nor deep enough to interfere with the general glossiness of the shell.

Very often these interstices are crossed longitudinally at unequal intervals by 20 to 25 faint ribs (sometimes no more than lines), which do not at all show upon the threads, and which die away at the periphery.

The inner lip is very sharp, and so far reflected and projecting as it advances downwards as almost wholly to conceal the columella, leaving a slight umbilical chink behind it.