A large collection of the Iberian millipede Cylindroiulus perforatus (Verhoeff 1905) has been examined. Examination of the gonopods revealed variation in the shape of the solenomerite which may have a regional basis. A distinctive feature of this species is the hole in the promerite. Some specimens were discovered which have entire promerites when examined using the electron microscope, although appearing perforated under the light microscope. These individuals do not appear to differ from the others in any other respects. An additional species in the perforatus-group from Portugal, C. fenestratus sp. n., is described which also has a perforate promerite, but differs from perforatus in the shape of the paracoxal process and the telson.