Observation of 24 cases of mating shows that usually it lasts about 60 seconds, and occurs between males with fairly hard shells and females with very soft shells (less than twelve hours after moulting). Correspondingly the males moult several weeks before the females. Of two males the one larger or superior in combat mates with the female. There may be repeated matings of one female with several males or of one male with several females. Preferably males should be slightly larger than females; if much larger mating rarely, if ever, occurs. At sexual maturity the two sexes are similar in size. Sperms retain their vitality in the female annulus for at least two years.