DESCRIPTION OF A MUSCLE SCAR AND 2 OTHER NOVEL FEATURES FROM STEINKERNS OF HYPOMPHALOCIRRUS (MOLLUSCA - PARAGASTROPODA)

Three novel features are described in steinkerns of Hypomphalocirrus r ugosus Linsley from the Middle Devonian Rogers City Limestone of Michi gan. The first feature is located about one-half a volution adapertura l of the terminal septum. It has the appearance of a typical molluscan muscle attachment scar and is interpreted as such. The two other feat ures are more enigmatic. They have a less stereotyped appearance and l ocation. The first is interpreted as a field of mantle point-attachmen ts and the other as a product of partial shell dissolution. Comparison s with extant and fossil molluscs confirm that the two features ascrib ed to biologic origins are within the scope of molluscan soft-part and shell attachment morphologies.