Unpacking a byte array into integers

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VB

Hi all. I've got an someArray(240) As Byte which I need to unpack into Int32 and Int16 integers. I know before I unpack:
1. that all data in someArray are integer values
2. what the startposition of each integer is in someArray
3. what the length of each integer is: Int32 or Int16

Currently I have a function which unpacks in the following way:

Function Unpack(someArray() As Byte) As Integer()
	Dim i32(4) As Byte
	Dim i16(2) As Byte
	Dim icount As Integer = 75

	Dim ivalues(icount) As Integer

	'field1: pos=0 len=4
	Array.Copy(someArray,0,i32,0,4)
	ivalues(0) = Int32FromByteArray(i32,bigEndian)

	'field2: pos=4 len=2
	Array.Copy(someArray,4,i16,0,2)
	ivalues(1) = Int16FromByteArray(i16,bigEndian)

	'field3: pos=6 len=4
	Array.Copy(someArray,6,i32,0,4)
	ivalues(2) = Int32FromByteArray(i32,bigEndian)

	'etc... until all 75 integers are unpacked from someArray

	Return ivalues
End Function

Functions Int32FromByteArray and Int16FromByteArray are functions which use the BitConverter class to convert from byte to integer taking into account that the number has to be re-ordered from BigEndian to LittleEndian.

Now I realize this is a very 'hard coded' way to unpack but I am able to do this because the positions and lengths of the integers in someArray are standardized.

My question: is there a way to unpack the byte array someArray directly into the integer array ivalues? Something like ivalues = someArray.SplitToInteger(someMask)?

Obviously the SplitToInteger function should do something more clever that my current Unpack function does. And obviously it should speed up the unpacking process.

Answers in C# are welcome too of course. Thanks in advance for your thoughts...

Follow-up 1:
I picked solutions 1, 2 and 4 but thanks for the reactions of everyone. I tested out the code of phil.o (solution 1) and it surely works in C#. I'm working now on the conversion to VB.NET which is not trivial because the bit shift operators work a bit differently for the two languages (for those interested: .net - Binary Shift Differences between VB.NET and C# - Stack Overflow). I will combine phil.o extensions with the Unpack function from F.Xaver in solution 4 but not use the BitConverter class for reasons of Endianess. I will post my wrap up in VB.NET here once I got the VB bitshi(f)t going. Tnx!!

Follow-up 2:
And here it is in VB.NET. The trick in VB with the bitshift is to cast byte first with CInt and then apply the shift (this was already mentioned in the article referenced above, but I didn't pick it up (late) last night).
The big and little Int32 extensions in VB.NET are (btw the name someArray has changed to traceHeader):

<Extension()>
Public Function GetInt32BigEndian(traceHeader() As Byte, pos As Integer) As Integer
	Dim result As Integer = CInt(traceHeader(pos+0)) << 24 Or _
		CInt(traceHeader(pos+1)) << 16 Or _
		CInt(traceHeader(pos+2)) << 8 Or _
		CInt(traceHeader(pos+3))
	Return result
End Function

<Extension()>
Public Function GetInt32LittleEndian(traceHeader() As Byte, pos As Integer) As Integer
	Dim result As Integer = CInt(traceHeader(pos+3)) << 24 Or _
		CInt(traceHeader(pos+2)) << 16 Or _
		CInt(traceHeader(pos+1)) << 8 Or _
		CInt(traceHeader(pos))
	Return result
End Function

I'm going to post a solution myself which I picked up, using Linq. I wonder what you have to say about that...?

Follow-up 3 and close out:

I have tested the answers processing a 6GB file containing 3,506,820 of byte arrays described above (called someArray and traceHeader). The results are:
1. for 3,506,820 traceHeaders using my original code: 48.04 seconds
2. for the same using solution 1 (bit shifting): 25.28 seconds
3. for the same using my solution 5 using linq: 185.31 seconds
So, solution 1 is the clear winner. My 'solution 5' with linq is not a solution.

Rgds and thanks