A couple of couesi (1 Viewer)

[Taphrospilus]

I thought Elliott Coues is perfectly solved but with German Wikipedia as Samuel Elliott Coues and English Wikipedia as Elliott Ladd Coues plus The Eponym Dictionary of Birds claim we have several options:

Coues's Flycatcher Contopus pertinax Cabanis & Heine, 1859 [Alt. Greater Pewee]
Coues's Arctic Redpoll Carduelis hornemanni exilipes Coues, 1862 [Alt. Hoary Redpoll ssp.]
Coues's Gadwall Anas strepera couesi Streets, 1876 EXTINCT
Rock Sandpiper ssp. Calidris ptilocnemis couesi Ridgway, 1880
Cactus Wren ssp. Campylorhynchus brunneicapillus couesi Sharpe, 1882
Dr Elliott B. Coues (pronounced 'cows'; 1842–1899) was a US Army Surgeon and one of the founders of the American Ornithologists' Union. Coues collected a warbler and asked Baird (q.v.) to name it in honour of his sister, Grace Darlington Coues (q.v.), hence Grace's Warbler. He is also the person who named the sandpiper after Baird. Amongst other works he wrote Handbook of Field and General Ornithology (1890), in which he set out in meticulous detail how to 'collect' and preserve birds, A Checklist of North American Birds (1873) and the 5-volume Key to North American Birds (1872–1903). Three mammals are named after him.

The Key to Scientific Names

Capt. Dr Elliott Coues (1842-1899) US Army surgeon 1863-1881, Professor of Anatomy, Columbian University 1882-1887, ornithologist, collector, spiritualist (subsp. Campylorhynchus brunneicapillus, subsp. Calidris ptilocnemis, syn. Garrodia nereis, ‡subsp. Mareca strepera, syn. Puffinus opisthomelas).

One obituary we can find e.g. in The Auk here

• Anas strepera couesi Streets, 1876 OD here
• Campylorhynchus brunneicapillus couesi Sharpe, 1882 OD here
• Calidris ptilocnemis couesi (Ridgway, 1880) OD here
• Oceanites nereis couesi Mathews, 1912 OD here
• Puffinus couesi Mathews , 1912 OD here

So is there an additional name and if yes which is the correct one?

 

[l_raty]

The Auk obit presents Samuel Elliott Coues as his father.

 

[l_raty]

Biographical details, suggesting Elliott Ladd Coues, at: Coues Family Papers – MS011
Also with "Ladd" on Geni: Capt. Elliot L. Coues, MD

Father: Samuel Elliott Coues (13 Jun 1797 - 3 Jul 1867). Grave: Samuel Elliott Coues (1797-1867) - Find A Grave...
Mother: Charlotte Haven Ladd (29 Sep 1813 - Jul 1900). Grave: Charlotte Haven Ladd Coues (1813-1900) - Find A...

But on his grave (as in his books -- and, so far as I can find, everywhere in the 19th C literature), he is just "Elliott Coues": Capt Elliott Coues (1842-1899) - Find A Grave...

 

[PScofield]

Definitely Elliott Ladd Coues but the only place I can find Ladd used is on the Birth registration and Baptism records - both are digitised but without image of originals:
Birth
09 Sep 1842 • Portsmouth, Rockingham, New Hampshire, United States
Baptism
14 Nov 1844 • Wakefield, Carroll, New Hampshire, United States