Like most Lafayette folks, I grew up eating crawfish every year. Either boiled, in an ettouffe, or however they were cooked, they were still craw-fish. Never have I ever referred to them as crayfish. On top of that I have always assumed crayfish was probably the official yankee term for the the edible crustaceans. Not so, as it turns out. I took a look at some archived pages in the Advertiser from May of 1958, and found that of the four seafood restaraunts in Lafayette that mentioned them, they were evenly split between crawfish and crayfish. At the Half Shell Restaraunt and the White Hut Restaraunt they were crayfish. Meanwhile over at Robert's Cafe and another restaraunt, who's name was obscured,  they advertised deep water crawfish. And, ironically, when looking on the net for information on this, the one with the skinny on the subject was in Illinois. Here's what they had.

 Nature Bulletin No. 405-A   February 6, 1971
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:CRAWFISH OR CRAYFISH?

Crawfish, or Crayfish? There are heated arguments about which is the 
correct name. The name crawfish was used in 1817 by Thomas Say, the 
first American zoologist to study these animals. Crayfish was coined by 
the English scientist, Thomas Huxley, about 50 years later. In this part 
of the country they are also commonly called "crawdad", "crabs" or, in 
the southern part of the state, "mudbugs ". Whatever you prefer to call 
them, there is hardly an acre of water in Illinois (unless it is the depths 
of Lake Michigan) or any acre of wet land, where these small 
freshwater relatives of the lobster are not found. About a hundred 
species are known in North America, of which a half dozen are 
abundant in this state.

From head to tail, a crawfish is crowded with a large assortment of 
appendages with special uses for each. In front are a pair of big saw-
toothed pincers for defense and capturing food; then four pairs of 
walking legs, two with small slender nippers and two without, also used 
for clinging, digging, handling food, and grooming the body. About the 
head are three pairs of "feelers" for exploring and warning of danger; a 
pair of beady black eyes on the ends of moveable stalks; three pairs of 
"jaw-feet" and three sets of jaws that chew sidewise. The flexible 6-
jointed abdomen ends in a flaring tail made up of five hinged scoops 
used for catapulting the animal, when alarmed, backwards in a 
smokescreen of mud.

As a rule, mature crawfish mate in winter and, in early spring, the 
females lay 200 or more shiny black eggs which are glued under her 
tail. These eggs hatch after a month or two and the young are carried 
there for another month before they let go of their mother's apron 
strings. Because the shell will not stretch, a crawfish must shed its shell 
and grow a bigger one, a dozen or more times before it is fully grown. 
After each molt, while it is still soft and flabby, it pumps itself up with 
water so that the new shell will be larger. Called "softshells" or 
"peelers" then, they are extremely helpless and hide until the new shell 
hardens. This is when they make the best bait for bass and other game 
fish. Most crawfish are mature after two years and 6 or 7 years is 
extreme old age. The length of our native adult ranges from 2 to 5 
inches, depending on the species.

Crawfish play an important role in Nature. Feeding on a wide variety of 
plants and animals, either dead or alive, they are the most efficient 
scavengers in fresh water. They make a superior food for about half of 
our fish especially for members of the bass family. The raccoon and the 
mink like them as much as anything else, and all sorts of water birds 
prey on them. Even the chimney-builders, that spend most of their time 
in the cool darkness of their burrows, must come out to eat and be 
eaten. Too few people realize that crawfish make fine eating: whether in 
salads like shrimp or lobster, in the famous crawfish bisque of the 
Creoles, or just boiled with a little seasoning for about 20 minutes. 
Connoisseurs eat the liver, as well as the meat in the tail, and down 
South they chant an old rhyme:

Yonder comes a man with a sack on his back -- Got all the crawdads 
he can pack. "

  Well, for me, that settles it. Crawfish forever! And, I think it would be a safe bet that no one below the Mason-Dixie line would ever call them crabs.