Stylianos Chatzimanolis recently described a new species of rove beetle among unidentified beetles in specimens borrowed from the Natural History Museum (London). In a paper published in Zookeys* ( Link to pdf ) he writes:

Upon further inspection, I realized that the specimen belonged to an undescribed genus and that it was Charles Darwin who had collected it on the Beagle’s voyage.

The beetle hails from Argentina and is one of two new species described in the manuscript. Not much is known about its natural history.
Darwinilus sedarisi a new species of rove beetle.
PHOTOGRAPH: NATURAL HISTORY MUSEUM, LONDON
*Stylianos Chatzimanolis. 2014. Darwin’s legacy to rove beetles (Coleoptera, Staphylinidae): A new genus and a new species including materials collected on the Beagle’s voyage. ZooKeys 379: 29–41.
doi: 10.3897/zookeys.379.6624