[PW] abbreviation of "John" ("Jno")?

[John Ptak]

Does anyone know the origin of the abbreviation of "John" as "Jno."?  Was this an abbreviation of a Latinized John, or for shorthand contraction for either a John or Jonathan?  Just curious...
Jno. Ptak
                        Specializing in rare and significant works in the history of science as well as indelible and iconic images.  
                  
                        J.F. Ptak  JF Ptak Science Books LLC & Longstreet Antiquarian Maps
                        8 Biltmore Avenue
                        Asheville, North Carolina
                        28801
                        USA  
                        jfptak at thesciencebookstore.com  tel:  828.254.0081  
                       
                 
            
     
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