Some examples of cistres
This image is from Corrette's Nouvelle Methode for mandoline. In fact the instrument depicted looks like a much older, seventeenth century form of cittern than a 1770s style 'Cistre Allemand'.
Here is a typical cistre made by le Blond (1773). Cistres were more ornately decorated than English guitars of the same era. The built-up rose and other decorations are reminiscent of some Baroque guitars. This instrument has some sort of a watchkey tuning mechanism and the holes through the neck (for a capo) can be seen.
A cistre rose and other decorations.
A plainer cistre this time with a second pegbox with two pegs (Deleplanque 1792). The tuning might have been the usual one for the fist pegbox and a low D and low A on the second. This cistre has a sort of keyboard attachment. Instruments like this in Britain were known as 'pianoforte' guitars.
An early cistre with a lute body made by Deleplanque (1764). This instrument has only ten pegs. Perhaps it is a six-course instrument with the tuning described by Corrette.
An arch-cittern (as they are sometimes called nowadays) with the typical configuration of eleven pegs on the first pegbox (for the usual seven-course tuning) and five more pegs in a second pegbox.
An unusual arch-cittern from 1787 with the body of the instrument extending right up one side of the neck as far as the nut. This was made by Renault and Chatelain in 1787.
Damien Delgrossi noticed this anonymous "Cistre francais XVIII siécle" as offered for sale by Rodolphe Delcroix of Nice. This instrument has an unusual body shape - like a Spanish guitar. The eleven pegs and the strings are arranged, as for a cistre, with four pairs and three singles. But the fingerboard is flush with the soundboard, like a Spanish guitar of the time , or a lute. The unvarnished top is surprising too. Perhaps it's some sort of hybrid.
Here is a photograph of a very elegant instrument by Laurent. The instrument is owned by Migheli Raffaelli and I am grateful to him for allowing me to use these images. The photographs were taken by Damien Delgrossi.
Seen from the front, one might have expected a lute body. But it has a flat back, curving towards the neck. It's a very deep-bodied instrument.
And here is the Laurent instrument next to a guittar and a Corsican cittern.