public void Main()
{
	var beBytes = new byte[] {
		0x80, 
		0x80, 
		0x80, 
		0x80, 
		0x80,0, 
		0x80,0, 
		0x80,0,0,0, 
		0x80,0,0,0,
		0x80,0,0,0,0,0,0,0, 
		0x80,0,0,0,0,0,0,0,
//		0x3F,0x80,0,0,
//		0x3F,0xF0,0,0,0,0,0,0,
//		0x30,0,0,0,0,0,0,0,0,0,
		0x54,0x65,0x73,0x74,0x69,0x6E,0x67,0,0,0
	};
	var leBytes = new byte[] {
		0x80, 
		0x80, 
		0x80, 
		0x80, 
		0,0x80,
		0,0x80, 
		0,0,0,0x80,
		0,0,0,0x80, 
		0,0,0,0,0,0,0,0x80, 
		0,0,0,0,0,0,0,0x80, 
//		0,0,0x80,0x3F,
//		0,0,0,0,0,0,0xF0,0x3F,
//		0x30,0,0,0,0,0,0,0,0,0,
		0x54,0x65,0x73,0x74,0x69,0x6E,0x67,0,0,0
	};
	Foo fooLe = ByteArrayToStructure<Foo>(leBytes).Dump("LE");
	Foo fooBe = ByteArrayToStructureBigEndian<Foo>(beBytes, 
		"bbbbsSiIlL"
//		+ "fd"		
		+"9bb").Dump("BE");
//	Assert.AreEqual(fooLe, fooBe);
}

[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct Foo  {
	public byte b1;
	public byte b2;
	public byte b3;
	public byte b4;
	public short s;
	public ushort S;
	public int i;
	public uint I;
	public long l;
	public ulong L;
//	public float f;
//	public double d;
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
	public string MyString;
}

T ByteArrayToStructure<T>(byte[] bytes) where T: struct 
{
	GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
	T stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(),typeof(T));
	handle.Free();
	return stuff;
}

T ByteArrayToStructureBigEndian<T>(byte[] bytes, string description) where T: struct 
{
	byte[] buffer = bytes;
	IList unpacked = DataConverter.Unpack("^"+description, buffer, 0).Dump("unpacked");
	buffer = DataConverter.PackEnumerable("!"+description, unpacked).Dump("packed");
	return ByteArrayToStructure<T>(buffer);
}

public void Main()
{
	var beBytes = new byte[] {
		0x80, 
		0x80, 
		0x80, 
		0x80, 
		0x80,0, 
		0x80,0, 
		0x80,0,0,0, 
		0x80,0,0,0,
		0x80,0,0,0,0,0,0,0, 
		0x80,0,0,0,0,0,0,0,
//		0x3F,0x80,0,0,
//		0x3F,0xF0,0,0,0,0,0,0,
//		0x30,0,0,0,0,0,0,0,0,0,
		0x54,0x65,0x73,0x74,0x69,0x6E,0x67,0,0,0
	};
	var leBytes = new byte[] {
		0x80, 
		0x80, 
		0x80, 
		0x80, 
		0,0x80,
		0,0x80, 
		0,0,0,0x80,
		0,0,0,0x80, 
		0,0,0,0,0,0,0,0x80, 
		0,0,0,0,0,0,0,0x80, 
//		0,0,0x80,0x3F,
//		0,0,0,0,0,0,0xF0,0x3F,
//		0x30,0,0,0,0,0,0,0,0,0,
		0x54,0x65,0x73,0x74,0x69,0x6E,0x67,0,0,0
	};
	Foo fooLe = ByteArrayToStructure<Foo>(leBytes).Dump("LE");
	Foo fooBe = ByteArrayToStructureBigEndian<Foo>(beBytes, 
		"bbbbsSiIlL"
//		+ "fd"		
		+"9bb").Dump("BE");
//	Assert.AreEqual(fooLe, fooBe);
}

[StructLayout(LayoutKind.Sequential)]
public struct Foo  {
	public byte b1;
	public byte b2;
	public byte b3;
	public byte b4;
	public short s;
	public ushort S;
	public int i;
	public uint I;
	public long l;
	public ulong L;
//	public float f;
//	public double d;
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
	public string MyString;
}

T ByteArrayToStructure<T>(byte[] bytes) where T: struct 
{
	GCHandle handle = GCHandle.Alloc(bytes, GCHandleType.Pinned);
	T stuff = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(),typeof(T));
	handle.Free();
	return stuff;
}

T ByteArrayToStructureBigEndian<T>(byte[] bytes, string description) where T: struct 
{
	byte[] buffer = bytes;
	IList unpacked = DataConverter.Unpack("^"+description, buffer, 0).Dump("unpacked");
	buffer = DataConverter.PackEnumerable("!"+description, unpacked).Dump("packed");
	return ByteArrayToStructure<T>(buffer);
}

http://stackoverflow.com/questions/2480116/marshalling-a-big-endian-byte-collection-into-a-struct-in-order-to-pull-out-value/2678472#2678472

See the URL for my question and answer on StackOverflow.

Byte Swapping Structs For Conversion From Big To Little Endian (Byte Order)

C#