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At least 5 more Mayfly species,  as well as one stonefly (Plecoptera), in addition to Rare and Endangered Accounts,  are worth considering :

1. Anepeorus rusticus McDunnough 1925,

Based on  adult males, the original description of this genus and species can be found on page 190 of the pdf below.  The description is based on three adult males, collected at Saskatoon, Saskatchewan in 1924.                                                                                Apparently, no more adults of this species  have never been seen.

anepeorus rusticus adult origianal mcdunnoughj1925p168.pdf

The larval stage of Anepeorus rusticus is unknown, but in the history of this species, Burks  1953 in Illinois found a larva of a mayfly which was lacking an associated adult, and,  on this basis,  he thought possibly the fuzzy, hairy, unique larva he had and which lacked and associated adult  might be the immature stage of Anepeorus-- and for this reason, the larva was called Anepeorus.  See also Edmunds, Jensen, and Berner, and the Lemsford Ferry page.

This turned out to be an error- I reared the larva of "Burks Anepeorus" and Eric Whiting and I found that the emerging adult was  Heptagenia cruentata

2. Raptoheptagenia cruentata Whiting and Lehmkuhl, 

See photos and more information at the Lemsford Ferry page, click Raptoheptagenia cruentata Whiting and Lehmkuhl.    From my field notes and collections, I first collected  larvae this species on 12 July, 1970, at Lemsford Ferry.  Two specimens were collected, 7 and 11 mm long respectively.  They were taken to the laboratory alive, and they readily fed on Chironomids held in forceps.  Additional specimens were collected at Lemsford Ferry on 21 June 1971.  They were found in fast water with a rubble bottom.  Sizes were 7 mm-2 specimens, 8 mm- 1 specimen, 9 mm- 1 specimen, 11 mm- 2 specimens.  In the lab they held on to stones and bark, they avoided sand, and they were very  awkward swimmers.   I reported them in Lehmkuhl (1976) as Anepeorus rusticus McDunnough- according to the literature and references of the time (e.g. Burks, and Edmunds Jensen and Berner). (.  Later, larvae were reared to adults, a new genus was described by us, and the new correct name is as above. Below is our original paper.

whiting and Lehmkuhl, Raptoheptagenia.pdf

3. Acanthamola pubescens Whiting and Lehmkuhl

Importand point. The larva of Anepeorus rusticus, above, is unknown.  and the adult of Acanthamola pubescens is unknown.  There is a good chance that they are one in the same , a  matching adult  and immature stage of the same species.  Rearing  of larvae to the adult stage will be required to answer the question.  However, both stages of the species are very rare.

Acanthamola Whiting and Lehmkuhl.pdf

Background information:  Larvae which are the holotypes for the above descrition were collected on July 12, 1970.  That was about 1 year after I arrived in Saskatchewan, and I had completed my survey of the South Saskatchewan river west from Saskatoon to the Alberta border.  Leader Ferry was not a good collecting site because of poor access and muddy substrates.  But Lemsford Ferry was an excellent site in all ways. 

Lemsford Ferry turned out to have an amazing variety of mayflies, and two of the species that I collected on July 12, 1970 turned out to be new  species and genera, Acanthamola pubescens Whiting and Lehmkuhl and Raptoheptagenia cruentata Whitting and Lehmkuhl.  Of course I did not know  until much later.

Regarding Acanthamola, I recall sorting the samples and noticing several small, white, apparently immature larvae with two caudal filaments, and flat bodies..  This is exactly the appearance of members of the common western genus Epeorus, so I labeled the specimens and set them aside in the Epeorus vial rack.   More than a decade later, while going through Alberta sample, Eric Whiting found these small larvae, but also noticed that they did not "fit"  the genus Epeorus.  The above paper resulted.

4. Choroterpes albiannulata McDunnough

more to follow

5. Traverella albertana (McDunnough) (see video).