This .NET class wraps the AcDbArcDimension ObjectARX class. 

That class represents an arc length dimension.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Entity
        Autodesk.AutoCAD.DatabaseServices.Dimension
            Autodesk.AutoCAD.DatabaseServices.ArcDimension

Public Class ArcDimension
Inherits Dimension

public class ArcDimension : Dimension;