Hello,
I have 2 of these knives in my collection.
Both of the were declared as rasor knives
Here You can see one of them:
http://cgi.ebay.de/ws/eBayISAPI.dll?...tem=6180735682
According to the wherabouts and the use of these knives I found several explanations in my literature.
Bernard Levine names them weaver's knives comming from Indiain his Guide to Knives and their Values .
Gabriel Mandel also names them weaver's knives but puts their origin to Bosnia Herzegovina.
In a book written by the well known Austrian collector Horst Brunner, these knives are named as tools for writing holy texts on palm leaves.
He puts their origin to Ceylon and dates them 19th century.
This description matches the one Mr. Toscani gave You.
This last description I could also find in the Solingen Klingenmuseum where one of these knives can be seen.
When I met Mr Brunner once in Solingen he showed me the knife which is displayed in Solingen.
Since I regard the knowledge and experience of Mr. Brunner I tend to believe his description concerning this kind of knife.
Greetings, Helge