Amphithalamus inclusus

The length of the shell attains 1.1 mm, its diameter 0.9 mm. (Original description) The shell has the habit of a minute Stenothyra W. H. Benson, 1856; the outer lip is not contracted, but the columellar lip um in adults travels forward to meet it, leaving a chamber behind. The nucleus is cancellated, and the base is bluntly ribbed. (Described as Amphithalamus stephensae) The shell is minute and pale brown with an ashy tinge, except for the columellar region, which is flesh-colored. When the animal is present, the early whorls appear much duskier. The nuclear whorls number 1.5; the first half is smooth, while the rest are marked by rather distantly spaced, poorly developed, rather broad spiral lirations, of which nine are present between the summit and the periphery. In addition to this, inconspicuous lines of growth are visible. Post-nuclear whorls and sculpture: The post-nuclear whorls are strongly rounded and narrowly shouldered at the summit, with the portion appressed to the preceding whorl appearing as a band through the substance of the shell. The periphery features a weak keel that is truncated rather abruptly posteriorly but grades gently into the substance of the shell toward the base. The suture is well marked. The base is short, inflated, strongly rounded, and marked by lines of growth only. …