Noun : r.    From Dictionary.com. 

The areas of visibility for 23 of these eclipses were conchoid and for 12 were cylindrical.    From Wordnik.com.  [The History of the Former Han Dynasty] Reference

The curves for the areas in which an umbral eclipse is viewed as partial are of two sorts: cylindrical and conchoid.    From Wordnik.com.  [The History of the Former Han Dynasty] Reference

The = pileus = varies from a regular wedge-shape to spathulate, or more or less irregularly petaloid, or conchoid forms, the extremes of size and form being shown in Figs. 112, 113.    From Wordnik.com.  [Studies of American Fungi. Mushrooms, Edible, Poisonous, etc.] Reference

For conchoid eclipses, outside the polar regions, that area extended from 1 to 2⅝ inches at right angles to the path of the umbral eclipse and from ⅜ to 1 inch from the ends in the direction of that path.    From Wordnik.com.  [The History of the Former Han Dynasty] Reference

I shall call such eclipses "conchoid.".    From Wordnik.com.  [The History of the Former Han Dynasty] Reference