Exception thrown: (Excel.Series)myChart.SeriesCollection(1)

[HeinrichMREx]

Hallo there,
why the following line in C#

Excel.Series mySeries = (Excel.Series)myChart.SeriesCollection(1);

throws the following exception

Exception Type:        System.InvalidCastException

What is the correct call in C# to get the series of a chart ?
If I try this way:

Excel.Series mySeries = (Excel.Series)myChart.SeriesCollection.Item(1);

I get the following compile error :

error CS0119: 'Microsoft.Office.Interop.PowerPoint.Chart.SeriesCollection(object)'

 is a 'method', which is not valid in the given context

Best,