The World Spider Catalog (WSC 2016) currently lists Peucetia longipes Pocock, 1899 as a senior synonym of P. casseli Simon, 1899; according to Niekerk & Dippenaar-Schoeman (1994: 16). The synonymy decision per se is not to be doubted but, regarding the senior name choice, it was stated that “As both P. [Peucetia] longipes and P. casseli were described in 1899, we decided to give P. longipes priority over P. casseli as the former species was more often referred to in the literature.” So Niekerk & Dippenaar-Schoeman (1994) did not check the month or even the day of the two relevant publications.
Dickinson, E.C. (2005) The Proceedings of the Zoological Society of London, 1859–1900: an exploration of breaks between calendar years of publication. Journal of Zoology, 266 (4), 427–430.
Duncan, M. (1937) On the dates of publication of the society's Proceedings, 1859–1926. Proceedings of the Zoological Society of London, A107 (1), 71–84.
ICZN [International Commission on Zoological Nomenclature] (2012) International Code of Zoological Nomenclature. 4th Edition. Incorporating Declaration 44, amendments of Article 74.7.3, with effect from 31 December 1999 and the amendment on e-publication, amendments to Articles 8, 9, 10, 21 and 78, with effect from 1 January 2012. Available from: http://www.nhm.ac.uk/hosted-sites/iczn/code/index.jsp (accessed 3 November 2016)
Milne Edwards, A. (1900) 41e réunion des naturalistes du muséum. 30 Janvier 1900. Bulletin du Muséum d'Histoire Naturelle, 6 (1), 1.
Niekerk, P. van & Dippenaar-Schoeman, A.S. (1994) A revision of the Afrotropical species of Peucetia (Araneae: Oxyopidae). Entomology Memoir, Department of Agriculture Republic of South Africa, 89, 1–50.
Pocock, R.I. (1900) On the scorpions, pedipalps and spiders from tropical West-Africa, represented in the collection of the British Museum. Proceedings of the Zoological Society of London, 67 (4), 833–885, pls. LV–LVIII. [for 1899]
Simon, E. (1900) Arachnides recueillis par M. Charles van Cassel, sous-officier d'infanterie attaché à la Mission du Cavally (Soudan françois), au poste du Zò, en septembre 1899. Bulletin du Muséum d'Histoire Naturelle, 5 (8), 416–419. [for 1899]
WSC (2016) World Spider Catalog. Natural History Museum Bern. Version 17.5. Available from: http://wsc.nmbe.ch (accessed 3 November 2016)