“Eupleura pterina” or Pterorytis dryas?

In 1947, Julia Gardner named two species of ocenebrines from the Alum Bluff Group. The first was “Pteropurpura dryas” from the Oak Grove Sand, now referred to Pterorytis (Microrhytis). The second was “Eupleura pterina” from the Shoal River Formation, which was named on the basis of only two specimens, which Gardner admitted might not be fully mature. Both species are shown in the image below.

Holotypes of "P. dryas" (9) and "E. pterina" (6) (images courtesy of the US Geological Survey)

In the ensuing years, much collecting has been done in both the Shoal River Formation and the Oak Grove Sand. We can now say with some level of confidence that the two species (P. dryas and E. pterina) are in fact one and the same. In fact, fragments of P. dryas are not rare in the Shoal River Formation, though complete adult specimens most certainly are. Juveniles of P. dryas in turn appear very similar in form to Gardner’s holotype of “Eupleura pterina.”

My best self-collected specimen of P. dryas was figured by Vermeij and Vokes in 1997, as well as by Portell et al. (2009). It now resides in the collections of the Florida Museum of Natural History. You can see FLMNH’s official photo of it here. The photo below is from my Fossil Muricidae website.

Pterorytis (Microrhytis) dryas (Gardner, 1947)

I have also figured below two sub-adult specimens of P. dryas, for the purpose of comparison with the holotype of “E. pterina.”

Pterorytis (Microrhytis) dryas (Gardner, 1947)

Pterorytis (Microrhytis) dryas (Gardner, 1947)

Pterorytis (Microrhytis) dryas (Gardner, 1947)

Pterorytis (Microrhytis) dryas (Gardner, 1947)

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References:

Gardner, J. “The Molluscan Fauna of the Alum Bluff Group of Florida,” USGS Prof. Paper 142-H, pp.525, 532-533, Plate LIII.

Portell, R. W., Polites, G. L., and Schmelz, G. W., “MOLLUSCA: Shoal River Formation (Middle Miocene),” Florida Fossil Invertebrates, Part 9, June 2006 (published by the Florida Paleontological Society).

Vermeij, G. J. and Vokes, E. H. (1997). “Cenozoic Muricidae of the Western Atlantic Region part XII — The Subfamily Ocenebrinae (In Part),” Tulane Studies in Geology and Paleontology, Vol. 29(3).