A recent discovery of a site with abundant roughly preserved Strobeus shells has piqued my curiosity for cutting them open to see the internal structure. The site occasionally preserves material with intact shells, but they are brittle and can shatter easily. During regular mashing of the limestone, they become disconnected, and their preservation is poor—attempts to free the shells carefully often produce the same results.

The structure of Strobeus varies over its many species, and the differences can be painstaking to detect. A matrix in the aperture often obscures the columnar fold. Removing the matrix is possible but can damage other features of the aperture. Strobeus lacks a nacre layer on its inner shell, thus making it prone to post-burial compression and breakage.

Knight’s Thin Sections

Knight (1931) presented thin sections of many named species in his review of the Subulitidae from the Pennsylvanian Outlier in St. Louis. I’ve had the privilege of reviewing one of these sections, but not one for Strobeus, then called Soleniscus (Macrochilina). My photos are not thin sections but provide similar detail. A thin section gives a better view of shell structures if they are preserved. Shells that have transformed to metastable calcite—such as these Portersville Limestone examples—often lack these features.

Strobeus thin sections by Knight, 1931
Figure 1—Thin sections of Strobeus by Knight (1931). A. S. primogenius (Conrad), B. S. paludinaeformis (Hall), C. S. brevis (White), D. S. medialis (Meek and Worthen), E. S. regularis (Cox). These are not type specimens and were selected by Knight as representative thin sections.

Three Cut and Polished Strobeus Specimens

The rest of this story can be told with photographs. Seeing the specimens cut, I am considering a study where I would cut and polish several specimens and study the internal structures. I want to compare the thickness of structures and make a note of shape, form, and details such as broken whorl walls.

Figure 2—A cut and polished specimen of Strobeus primogenius.
Figure 2—A cut and polished specimen of Strobeus primogenius from the Portersville Limestone in West Virginia. CG-0640. Scale bar = 5 mm.
A cut and polished specimen of Strobeus sp
Figure 3—A cut and polished specimen of Strobeus sp from the Portersville Limestone in West Virginia. While this shows a classic Strobeus form, a species cannot be assigned without a view of the column. The shell walls appear unusually thin in the middle portion. Specimen ID CG-0663 Scale bar = 5 mm.
A cut and polished specimen of Strobeus primogenius.
Figure 4—A cut and polished specimen of Strobeus primogenius from the Portersville Limestone in West Virginia. The columellar fold is broad, and its reabsorption in earlier whorls is apparent. The bottom portion showcases features of the Portersville Limestone at this location. Specimen ID CG-0667. Scale bar = 5 mm.

And Last, a cut and polished Euphemites callosus

A few specimens of this gastropod appear in the Portersville Limestone and are often very large. The shells are difficult to free beyond whatever portion is sticking out of the limestone during recovery. Trace fossils littered the specimen below, making shell detail challenging to see, and I considered cutting vs storing as-is.

Figure 5—A cut and polished specimen of Euphemites callosus. The variety of infill material is interesting. Tract burrowing fossils littered the shell surface, and a few are visible on the top right shell surface, Specimen ID CG-0661.

More Cut Fossil Gastropod Specimens ✂

References