In July 1944, Ōyama moved to the Imperial Navy's Macassar Research Institute in present-day Indonesia, working as a researcher until the Institute's dissolution in May, 1946. Thereafter he returned to Tokyo and resumed his position at the Natural Resources Institute. In 1947, he took up a concurrent position at the Geological Survey of Japan. Ōyama received his PhD in 1955, and almost immediately left for a period of postdoctoral research with Dr. Myra Keen at Stanford University in California that lasted until April 1957. In 1979, Ōyama retired from the Geological Survey and founded a research laboratory at Toba Aquarium in Mie, also housing his vast library of paleontological and malacological literature.
Publications
Ōyama was a prolific author, both independently and in collaboration with others. Between 1959 and 1963, he published a six-part photographic catalog of many Japanese molluscan families, co-authored with Yoshio Takemura. Together with Tadashige Habe and Tokubei Kuroda he was commissioned by the publisher Maruzen to co-author The Seashells of Sagami Bay on behalf of the Imperial Household. Ōyama's collected papers were republished in two volumes, one to celebrate his 70th birthday in 1987 and one for his 77th in 1994. A memorial volume of reminiscences and photographs appeared in 1996, following his death on December 30, 1995.
Personal life
A lifelong bachelor, Ōyama was fluent in English and French. Like many of his contemporaries, he insisted on his name being cited in English using its Kunrei transliteration "Katura". He was a co-founder of the Malacological Society of Japan, and attended its annual meetings until 1994. He was latterly a frequent guest at the monthly meetings of the Hanshin Shell Club in Nishinomiya, Hyōgo Prefecture, together with other former members of Tetsuaki Kira's post-war Tengu-kai club.
The Ōyama Library
Ōyama built up a massive personal library of books and papers on Paleontology and Malacology that included many major nineteenth-century western works and a substantial body of Russian literature. Following his death this was held in storage at Toba Aquarium for many years, before being transferred to the Osaka Museum of Natural History at Nagai Park in 2013.
