see Bradleya 11:109. 1993. Email from Urs Eggli on volume numbers: Cactaceae etc. right from the beginning in 1991, has a double volumation count – the volume for 1991 is at the same time vol. 1 and vol. 11 (the latter presumably continuing the volumation of its predecessor). I also checked our copy of the volume for 1996, and this has the volume count as 6 / 16.