Page:Scientific results HMS Challenger vol 18 part 2.djvu/560

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Definition.— with the terminal mouth of the shell open (vel Stichocyrtida triradiata aperta).

Definition.— (vel Stichocyrtida triradiata aperta) with three solid lateral ribs or wings, without terminal feet. Cephalis with a horn.

The genus Stichopilium is the most primitive among all Stichocyrtida, and represents perhaps the common ancestral form of this family. The shell is composed of four or more joints (sometimes ten to twelve), has a wide open terminal mouth, and three lateral solid wings or ribs (sometimes a little latticed on the base). Stichopilium may be derived from Theopilium or Pterocorys by addition of new terminal joints.

Definition.—Shell with three annular strictures, and four distinct joints.