You can use a snippet (for example, in Application_Start), to understand, what IOS expects.
Code:
Dim no As NativeObject
Dim l1 As List = no.Initialize ("UIFont").GetField ("familyNames")
For Each s1 As String In l1
Log (s1)
Dim l2 As List = no.Initialize ("UIFont").RunMethod ("fontNamesForFamilyName:", Array (s1))
For Each s2 As String In l2
Log (" " & s2)
Next
Next
In your case you will see for family name Futura LT following font names:
Code:
FuturaLT-Book
FuturaLT-BookOblique
FuturaLT-Bold