ephemorids
Note from Robert Ross , a Chapter from Anecdotes about 20th Century Authors

Sitwell seems to be trying to change the adjective 'ephemoral' into a noun, but he is mistaken. 'Ephemorides' does not mean transitory but

A journal or account of daily transactions; a diary; a publication exhibiting the places of the heavenly bodies throughout the year, and giving other information regarding them; an atronomical almanac; a collective name for reviews, magazines, and all kinds of periodical literatureThe New Webster Encyclopedic Dictionary of The English Language (1952)