reason alone, competing with Hahn's new project was already impossible. So not surprisingly, the promised ninth installment failed to appear. In the past, some confusion arose regarding the year of publication, particularly of the installments 2, 5, and 7, probably caused both by the partial absence of dated forewords and of dust jackets for the individual installments, as by the fact, that the bookshop and later (1822) publisher, Lechner did not only provide installments that were sold later with a nonoriginal cover, but in a good many cases also overwrote the year of publication with the year of sale. On basis of recent investigation, the correlation between installments and the years of publication has been clarified as: A definitive representative copy of "Monographie der Spinnen" probably does not exist (any more). The available copies differ in several features as detailed pointed out by Sacher. For this reason, it was used a combined version for the reprint of 1988. [[Image:Eresus annulatus et cinnaberinus (Hahn 1821, 2).jpg|thumb|200px|"Eresus cinnaberinus, Walk." and "Eresus annulatus, mihi sensu, Hahn 1821, installment 2]] "Monographie der Spinnen", though, is far more than just a bibliophilic work. Firstly, it includes nine still-valid first descriptions of spider species. In the 19th century not unusually, a majority of "new species" had been previously described by other authors, because in contrast to the modern differentiation of species, the genital structures were not taken into consideration at that time. For that reason, smaller differences in the colourings and markings have possibly given rise to different species designations. At any rate, a sixth of the forms described by Hahn are still valid today. That Hahn was a good observer and gave exact descriptions is shown clearly by the example of Eresus annulatus (= E. sandaliatus (Martini & Goeze>, 1778)) and E. cinnaberinus (= E. kollari Rossi, 1846). After more than 150 years, arachnologists follow his separation of these taxa today again. Secondly, its monographic character is remarkable. It is the first monographic work for spiders in the German language. Further, 180 years ago, using a group such as spiders as a sole subject of a book was very unusual. Apart from a natural history of spiders by Frenchman <Walckenaer in 1806, no work of that time has exclusively had spiders as its subject. Thirdly, spider illustrations in the "Monographie der Spinnen" show Hahn to be an above-average artist and lithographer. Finally, "Monographie der Spinnen"