Ellis L. Yochelson

Paleozoic Mollusk: Hyolithes

An unusually well-preserved Ordovician fossil from Czechoslovakia shows that the enigmatic paired structures once thought to be outgrowths of the operculum of Hyolithes are really independent structures lying between the operculum and the aperture of the shell. The find seems to provide conclusive proof of the morphologic uniqueness of hyolithids.

POLYPLACOPHORAN MOLLUSCS OF THE ESSEX FAUNA (MIDDLE PENNSYLVANIAN, ILLINOIS)

ABSTRACT Several hundred specimens of Pterochiton concinnus (Richardson) have now been collected from the Mazon Creek area. All are articulated, and most show all eight valves, held in place by a girdle, the margin of which is heavily spiculate. Most specimens preserve the radula, which is remarkably similar to that of living specimens.

The youngest styliolines and nowakiids (Late Devonian) currently known from New York

This is the first report of styliolines in the Angola Shale Member of the West Falls Formation in western New York. These specimens are of late Frasnian age and are the youngest individuals known from the Appalachian Region. This upward extension of range places the extinction of styliolines in eastern North America more in accord with their time of extinction in Europe. Nowakiids have also been found in the younger Hanover Shale Member, in the upper part of the Java Formation, also of late Frasnian age. These are the youngest known nowakiids from the Appalachians. Within the limits of preservation, the external characters and wall structure of the Angola styliolines are comparable with those of older specimens. The associated rare small annulated nowakiids and homotcenids have a laminated wall structure fundamentally different from that of the styliolines.

GASTROPODA OF THE ESSEX FAUNA, FRANCIS CREEK SHALE (MIDDLE PENNSYLVANIAN), NORTHEASTERN ILLINOIS

Study of more than 140 siderite concretions from the Francis Creek Shale of Savage (1927) (Middle Pennsylvanian) in northeastern Illinois shows Euphemites to be the most abundant form. A new species, E. richardsoni , is described from the Pit Eleven locality in Will and Kankakee Counties. Strobeus is the next most common gastropod, but all specimens are imperfectly preserved. Two specimens of Straparollus (Euomphalus) sp. are available. Hypselentoma sp. and N. (Naticopsis) sp. are both represented by single specimens. None of these specimens is sufficiently well preserved to permit formal description. When compared with other midcontinent Pennsylvanian gray shales, the Essex biofacies of the Francis Creek Shale is characterized by low density, low diversity, and low evenness among marine gastropods.