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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Mayfly Genus Penelomax

This recently minted genus contains a single, very distinctive species, Penelomax septentrionalis. Visit that page for information.

Where & when

In 19 records from GBIF, adults of this genus have been collected during June (74%), July (16%), May (5%), and November (5%).

In 4 records from GBIF, this genus has been collected at elevations of 341, 361, 2152, and 2441 ft.

Genus Range

Specimens of the Mayfly Genus Penelomax

1 Female Dun
2 Nymphs

Discussions of Penelomax

Anyone know more about Ephemerella septentrionalis?
11 replies
Posted by Troutnut on May 18, 2007 in the species Penelomax septentrionalis
Last reply on Jul 18, 2011 by Oldredbarn
I found about one sentence on these in Gonzo's book, and haven't seen them mentioned anywhere else in fly fishing literature. Nor is any of the scientific literature I have on them particularly interesting (just descriptions). Now that I've collected a few and see what unique-looking nymphs they've got, I'm really curious about them.

Start a Discussion of Penelomax

References

Mayfly Genus Penelomax

Genus Range
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