page_title: Potamolithus rushii
section_title: Life cycle
hierarchical_section_title: Potamolithus rushii / Life cycle
caption_attribution_description: English: Drawing of an apertural view of a juvenile shell of Potamolithus rushii.
context_page_description: Potamolithus rushii is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Lithoglyphidae.
  Potamolithus rushii is the type species of the genus Potamolithus.
  The specific name rushii is in honor of Dr. William H. Rush, who collected this species.
context_section_description: The youngest specimens seen by Pilsbry had three whorls and a diameter of 3 mm. They had the depressed contour of adults and were strongly carinate peripherally, but the carina is distinctly weaker in front of the mouth, apparently indicating that it begins when the shell has nearly two whorls and a diameter of about a millimeter. At the 3 mm stage, the columella is very broad, semicircular, with a deep excavation and rod-like inner border (see image on the right). Very late in the neanic stage the basal keel appears, the shell then being about 5 mm in diameter; the columellar area is very narrow, at first linear. The rib or convexity of the upper surface is also of late appearance, these structures belong to the third neanic substage, the second, or unicarinate, substage thus occupying the greater part of the neanic stage. The discontinuation of the upper ridge or hump initiates the ephebic substage. The marginal varix and the absence of any tendency of the last whorl to descend or loosen its coil anteriorly, show that this species is at its acme. It has none of the stigmata of senility which are so manifest in Potamolithus microthauma, Potamolithus hidalgoi, etc.
caption: apertural view of a juvenile shell
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