Unfortunately, Dall rarely gave derivations for the names he introduced, and
he did not give one for Typhis latipennis. However, the description of the
species includes the phrase "terminal varix wide". "Penna" in Latin means
wing or feather ("pinna" is a related word with additional meanings like
"pen"). So I would translate "latipennis" as "broad-winged", by analogy to
the common name of the Broad-winged Hawk, Buteo platypterus.
 
Andy said that he doesn't see how "pennis" can be derived from "penna". I
had the same objection ("pennis" is not the nominative or genitive form of
"penna"), but I've just found in the Oxford Latin Dictionary that the suffix
"-is" is used to form compound adjectives from nouns. Here's another avian
example: the Great Auk, Pinguinus impennis.
 
Gary