 Clark is most notable for describing the dinosaur ant (Nothomyrmecia macrops), which is the most primitive living ant in the world and second most primitive when the fossil record is included. The first collection of Nothomyrmecia was made in December 1931 by Amy Crocker who collected specimens of two worker ants, reportedly near the Russell Range from Israelite Bay in Western Australia. Crocker sent the two specimens to Clark at the museum for study; in 1934, Clark published a formal description of Nothomyrmecia as a completely new genus of the Myrmeciinae. He did so because the two specimens (which then became the syntypes) bore no resemblance to any ant species he knew of, although they did share similar morphological characteristics with the extinct genus Prionomyrmex. This unusual ant remained unknown to scientists, causing intense scientific interest in the early 1950s. Over three decades, however, teams of Australian and American collectors failed to re-find it after they initiated a series of searches. Then, in 1977, entomologist Robert Taylor and his party of entomologists from Canberra found a solitary worker ant at Poochera, southeast of Ceduna, some 1,300 km (810 mi) from the reported site of the 1931 discovery. After 46 years of searching for it, entomologists have dubbed the ant the "Holy Grail" of myrmecology. Such discovery of Nothomyrmecia and its general nature marks it as one of Clark's most notable achievements.
