The archives of the French national library are quite complicated, with several interlinked websites; it surely helps if one is mastering the language to get around and eventually find what you were after.
Books of hours were devotional books in the Middle Ages, which were in fact illuminated manuscripts containing a collection of texts, psalms and prayers. They were usually abridged versions of breviaries in use in monasteries, and each book of hours is unique and especially the ones made for wealthy persons are lavishly decorated. Antoine ‘le Bon’ (1489–1544), Duke of Lorraine, was the one for whom this manuscript was made.
This manuscript  consists of 93 folios. There are two copies of this document present on the Gallica website, which differ in their pagination; the search result list  contains a double entry due to this entanglement. The copy used may be found here .
Snails may be seen on several folios:
f. 7v: in the upper border, a side view with the head pointing to the right, the left-coiled shell is seen from dorsal; the stylised snail has a humanised face (eye, mouth) and only one pair of tentacles is indicated.
f. 9r: upper border, a stylised snail with a human eye and one pair of tentacles, the shell shown dorsally; I call this the ‘sitting on its tail’ posture.
f. 14r: in the lower border a variation on the theme ‘knight v. snail’  is seen. The stylised snail, left-coiled, with four tentacles and a human eye but without tail, emerges from the neck of a dragon-like bird and is opposed to a man with a stick, who seems distracted by a hybrid figure at left.
f. 15v: right-hand border, stylised snail, with one tentacle and humanised face is being lifted above a woman above her head.
f. 24v: upper border, a stylised snail, two tentacles and an eye at the base, without tail; the shell is shown dorsally.
f. 47r: lower border at right from the coat of arms, a stylised snail with two tentacles and a humanised face, without tail; the shell is figured upright and from the dorsal side.
f. 49v: upper border, a stylised snail, the shell light coloured and in dorsal view, the animal with a dark body and a humanised eye but without tentacles.
f. 61r: in the lower border two snails, one of each side of the coat of arms. Both are stylised, with one tentacle and a humanised eye, the shell seen dorsally with an impression of strong striation; the animal is in the same tone as the shell and figured from the side. The left snail is normally coiled, the right one is left-coiled.
 http://en.wikipedia.org/wiki/Antoine,_Duke_of_Lorraine (03-01-2014); the portrait is by Hans Holbein the Younger.
 BNF, Ms. Nouvelle acquisition Latin 302, http://bit.ly/1dsD2sh (03-01-2014).
 http://bit.ly/1cpVqRs (03-01-2014).
 http://gallica.bnf.fr/ark:/12148/btv1b525017457 (permalink).
 Biggs, S.J. (2013): Knight v. snail. Http://bit.ly/1anPrw0 (25-10-2013).