Page:Scientific results HMS Challenger vol 18 part 2.djvu/592

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

Definition.— (vel Stichocyrtida eradiata aperta), with conical shell, gradually dilated towards the wide open mouth. Cephalis with a horn.

The genus Lithostrobus is probably the most primitive among the Lithocampida, and comprises those forms of this family in which the slender, conical shell is gradually dilated towards the wide, terminal mouth, each joint being broader than the preceding.