UGA Stratigraphy Lab

The data is in the strata

Gryphaea

Species

Gryphaea impressimarginata McLearn, 1924
Differs from G. nebrascensis in being more robust and having coarse ribbing on umbo. Elongate to subtrigonal outlien, with convexity ranging from moderate to strong.
Occurrence: Sawtooth (common at top, uncommon in base), Rierdon (base), Twin Creek (lower)
Reference: Imlay, 1948

Specimen Photo

Gryphaea impressimarginata
Photograph from Imlay, 1948

Gryphaea nebrascensis Meek and Hayden, 1861
Elongate shale, prominent and narrow umbo, strongly incurved beak, with radiating striae on umbo
Occurrence: Extraordinarily abundant in the Stockade Beaver Shale, ranges to top of marine Jurassic
Reference: Imlay, 1948

Specimen Photo

Gryphaea nebrascensis
Photograph from Imlay, 1948

Gryphaea planoconvexa Whitfield, 1876
Subcircular, with moderately inflated left valve
Occurrence: Sawtooth (middle), Piper (middle), Gypsum Spring (middle), and Twin Creek (basal)
Reference: Imlay, 1948

Specimen Photo

Gryphaea planoconvexa
Photograph from Imlay, 1948