1: pink prostate and ciliated field visible through translucent mantle.
2: mantle edge.
3: head.
4: filament of penis.
5: mamilliform glands of penis.
6: base of penis.
7: mucronate tip on broad rounded distal end of penis.
Characteristic typical penis of L. saxatilis, diagnostic when present, but sometimes variation in form overlaps with that of L. arcana when dead or on a live anaesthetized/relaxed specimen. “It is noticeable that the penis tip of L. rudis [=L. saxatilis s.s.] is frequently mucronate [broadly rounded with a small short apex]. This never occurs in L. arcana in which the tip tapers to a point. – – – That it is not always readily apparent in penes of L. rudis could be due to the killing [or relaxing] technique affecting the contraction of particular muscles” ( Hannaford Ellis, 1979).

Explanation of “mucronate” at eflora.library.usyd.edu.au/glossary/mucronate

Specimen B.
Comparison of images in this Flickr collection will show that penes are usually far more elongated on live un-anaesthetized specimens, and can be held in a variety of positions. Observing the tip on live physically restrained animals is possible, but requires patience as it is usually the last part to be brought out of the shell.
For practical identification, if a clear mucronate tip is visible, the animal is L. saxatilis s.s.. But if it is absent on dead or relaxed specimens, or not exposed on a live one, it cannot be assumed it is definitely L. arcana, though it remains a good possibility.

No full account yet of this species.
marinvert.senckenberg.science/image-browse/7215763361…