1915: two-year-old season Clarissimus showed very promising form on the training gallops and was highly regarded by his trainer, but on his racecourse debut he was well beaten by the
fillies Telephone Girl and
Fifinella in the Bibury Stakes ant Newmarket. At the same track in October he recorded his first success in the Clearwell Stakes.
1916: three-year-old season Clarissimus performed well in training in the spring of 1916 although his trainer's confidence was somewhat dented when his galloping companion, a filly named Angelina, ran poorly in the
Greenham Stakes. by three quarters of a length from Kwang-Su with Nassovian half a length away in third place. In the
Newmarket Stakes over ten furlongs on 17 May, Clarissimus was beaten half a length by Figaro. He had a particularly bad race and did not recover sufficiently to take part in the
"New Derby". After a break of almost four months, Clarissimus returned for the September Stakes at Newmarket, a substitute race for the
St Leger. He proved to be no match for the favourite
Hurry On but took second place, five lengths clear of Atheling in third place. after the late withdrawal of
Pommern. Ridden by the Australian jockey Frank Bullock, he had "no difficulty" in winning from the four-year-old filly Silver Tag. ==Assessment and honours==