Numpy: np.iinfo（ 'head'）が失敗する

>>> np.iinfo('intc')
iinfo(min=-2147483648, max=2147483647, dtype=int32)
>>> np.iinfo('uintc')
iinfo(min=0, max=4294967295, dtype=uint32)
>>> np.iinfo('longlong')
iinfo(min=-9223372036854775808, max=9223372036854775807, dtype=int64)
>>> np.iinfo('ulonglong')
iinfo(min=0, max=18446744073709551615, dtype=uint64)
>>> np.iinfo('long')
iinfo(min=-9223372036854775808, max=9223372036854775807, dtype=int64)
>>> np.iinfo('ulong')
Traceback (most recent call last):
  File "<ipython-input-20-e783aa7ef3c1>", line 1, in <module>
    np.iinfo('ulong')
  File "/home/antoine/miniconda3/envs/pyarrow/lib/python3.6/site-packages/numpy/core/getlimits.py", line 516, in __init__
    raise ValueError("Invalid integer data type.")
ValueError: Invalid integer data type.