A monograph of the Gymnoblastic or Tubularian hydroids by George James Allman, published in 1870. I found this book in the library of the Tjärnö laboratories in Sweden. Allman was a pioneer in hydrozoan research and described many species. Nowadays it is much easier to access original descriptions since many book are available online. You can find a PDF of this book in the Biodiversity Library. Picture credits: Lara Beckmann