In the middle of the operculum, and posterior to it is the genital appendage.  There are 2 types of genital appendages, suggesting sexual dimorphism.  Type A has more pronounced spermathecae, or horn organs suggesting that it belongs to the female.  Type B is shorter and it is thought that it belongs to the male.  Previous schools of thought had the clasping structure down as diagnostic of the male.

The male would have transferred a sperm package (spermatophore) onto the substrate which would have then been picked up by the female for storage in the spermathecae.  The spermatophore may have been picked up via movement of the gills in the female.