In the course of time I have come to a cabinet-and-a-half containing a couple of thousand lots of a family of snails (gastropods) named Cerionidae. Though there are four genera in the family, the Delaware Museum of Natural History holds members only of the type genus Cerion. The family was split out from a large family, Urocoptidae, by Henry A. Pilsbry in 1901. "Harry" Pilsbry spent much of his career at the Academy of Natural Sciences in Philadelphia, where he described hundreds (thousands?) of new species.
This first photo is of the type species (of the type genus of the family Urocoptidae), Urocoptis cylindrus (Dillwyn, 1817). Lewis Dillwyn originally named this species Turbo cylindrus, using a genus name created by Carl Linnaeus in 1758, when he single-handedly invented biologic nomenclature. At the time these specimens were collected the species was considered of the genus Cylindrella, then was shifted again to the genus Urocoptis when the family Urocoptidae was set up. The family Urocoptidae contains many genera, and while many of the species are similar to this one, being cigar-shaped with a flaring aperture, they vary a lot around this gestalt.
The genus Cerion, pronounced "kerion" or "Syrian", from the Latin word cerea, meaning "waxy", was named by Peter Röding in 1798, based on his renaming of Turbo uva as Cerion uva (Linnaeus, 1758). The genus has just a handful of fully accepted species, but the DMNH collection contains representatives of more than 200 species, which have varying levels of acceptance among workers carrying on a decades-long reworking of land snail families. This photo shows two characteristics of many Cerion species: the off-white waxy color and the ribbing along the entire shell. The flared aperture is less pronounced than it is in most of the Urocoptidae. The following photos showcase three more Cerion species, chosen to illustrate the range of variation in the genus.
The photo below shows Cerion weinlandi (von Martens, 1860); Edward von Martens originally placed it in the genus Pupa. It does look like a pupa! I chose this species to illustrate the extreme of nearly absent ribbing. Also, while the background color tends to be waxy off-white, this species is one of many with color banding and mottling also.
Though this lot is labeled Ceriod dalli Maynard—publication date is probably 1889—it was renamed and included in the species Cerion rubicundum (Menke, 1829). I don't know what name Karl Menke originally gave it. The species name means "ruddy", and when the shells are fresh and moist, the brown markings are reddish-brown. I chose this species for its narrow ribbing.
Finally, Cerion marielinum Pilsbry, 1927 (the museum curator attributed the species to Carlos de la Torre, who had edited the journal in which Pilsbry published the description) is so named for its occurrence mainly near Mariel, Cuba. This species shows wider, more robust ribbing, and also has a ruddy background with the waxy white being confined to the tops of the ribs.
I chose the scale for these photos so that they would show the shells close to life-size on a 17-inch monitor. On my 22-inch monitor they are about 25% larger than life. Comparing the four Cerion species with Urocoptis cylindrus, there is certainly a resemblance. It is easy to see why the genus was originally put in the same family. However, details of their morphology, including not only the more pronounced ribbing, but also the smaller aperture and the small teeth inside the aperture, distinguish Cerionidae from Urocoptidae…at least for now! Biological naming is always a tug-of-war between "splitters" and "lumpers". In some mollusk families, large numbers of species have in recent years been combined into a relative handful of species, and this may soon result in the few hundred species of Cerion being lumped into a smaller number of species that are recognized as being rather variable.
Genetic studies and breeding studies are going on in parallel, and revealing more and more about the species and inter-species relationships of many animals, not just snails. But, you know, I just like opening a drawer full of shells once in a while to simply admire them.
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