Indeed, every single Carcano model had provisions for its accompanying bayonet. We can distinguish the following models, taxonomically:
M/91 rifle bayonet ("schiabola-baionetta"):
This, in its various scabbards, is the most commonly encountered today: its form is "classical", sand lightly reminds of the Finnish M 27, M 28 and M 28/30 bayonets. The crossguard is straight, like a sword, and in English edged weapons terminology, it would be best called a "sword bayonet".
M/91 Moschetto T.S. bayonet:
The first main "Carbine for special troops" bayonets (the earliest Moschetti TS had used the ordinary rifle bayonet) are peculiar and easily identifiable by their quaint transversal locking lug arrangement going through the pommel from left to right. They are somewhat rare and command about 50% surcharge on ordinary sword bayonets. Otherwise, they are almost identical.
M/91 Moschetto per Cavalleria bayonet:
This is a permanently attached fixed folding bayonet: its narrow T-section spike is hinged to a block at the muzzle (which also takes the front sight) and folds back under the barrel and into a slot on the lower side of the stock. The Japanese cavalry and paratroopers' carbines used a similar arrangement. Many variations of the locking mechanism exist: Richard Hobbs has counted at least nine.
The three main variations are, in order of historical appearance:
M 1938 knife bayonet ("pugnale-baionetta"):
Only this short model should be called "knife bayonet", since it indeed evoked a knife or short dagger. It is patterned after the example of the fascist daggers (pugnali), was a popular war souvenir with US soldiers and even today is the Carcano bayonet most sought after, especially in its first variant.
It was a curious design: a folding-blade knife which however was to be kept attached at the muzzle of the rifle. The knife blade would fold back into the stock when not in use (this is the reason for the slotted nosecap of the Fucili M 1938), and could be folded out in case of necessity. Why one made it at all attachable instead of keeping it fixed as with the cavalry carbines is not entirely clear - probably to provide for the case that a soldier would need his bayonet for the (much more common) use of opening tin cans, slaughtering the requisitioned chicken or rabbits, or even for the (rarer) use as a fighting knife in close combat. It appears that the folding-blade gimmick was not of much use since the bayonet soon lost its folding mechanism and ultimately was made up completely fixed.
The following types can be distinguished:
For all the sword bayonets, two types of frogs exist: the simple bayonet frog, and the larger frog with an additional compartment and a buckled securing strap for the entrenchment tool.
And here is a link to a picture listing of a number of Italian bayonets: http://www.inil.com/users/driver/Bayonets%20for%20sale.htm#ITALY