Flexicalymene retrorsa

I use this page to compare my published photographs with the literature, not to turn a quarry name into an identification.

Start with the head, not the locality

The Atlas of Ordovician Life describes the Flexicalymene glabella (the central raised part of the head) as tapering forward, with three pairs of deep lateral furrows separating rounded lobes. These are genus-level comparison features, not a diagnosis of F. retrorsa on their own.[6]

Ross’s 1967 comparison of F. meeki with material assigned to F. cf. retrorsa emphasizes the anterior border: the rim in front of the glabella. His cf. retrorsa specimen has a narrow border turned upward to nearly vertical; the meeki border is wider front-to-back and less steeply inclined.[8]

Ross used a qualified identification (cf. retrorsa) for the illustrated comparison specimen. I retain that qualification here: this historical comparison is useful, but it does not independently verify the names on my records.[8]

Published locality evidence is separate

The Paleobiology Database lists Flexicalymene retrorsa in collection 192315, referencing Key and colleagues (2010). Its collection record names the Mt. Orab Trilobite Shale Bed and records the formation as Arnheim.[7][9]

That published locality record is not verification of any individual fossil below. The names and confidence labels below are my recorded identifications; they are not conclusions reached by those authors.

A literature comparison to check against an exposed head[8]
Feature to inspect	F. cf. retrorsa in Ross (1967)	F. meeki in Ross (1967)
Anterior border, seen from the side	Narrow front-to-back; upturned to nearly vertical	Wider front-to-back; less steeply inclined

How I inspect a specimen

Open a full-size photograph, then locate the front rim of the head. Compare a side view with a view from above rather than judging from one angle.
Check whether that rim is exposed, obscured by rock, broken or distorted. If it cannot be followed clearly, record the feature as not observable rather than treating the missing view as a match.
Use close-ups to compare the head’s central lobes and furrows with the genus description. Keep that genus-level comparison separate from the border comparison used for species.
Keep field and prepared views together when both exist. Preparation may make a feature easier to inspect; a new view is not, by itself, a new taxonomic determination.