Carolyn Bartlett Gast has been drawing animal specimens at the Natural History Museum for the past 30 years. During that time, she has found herself lusting after lobster and foiled by fish scales.

When she was illustrating lobsters from preserved specimens at the Smithsonian, she found herself spending a lot of money to satis her appetite for lobster dinners after work.

And the fact that a particular fish was caught by a fisherman who dragged it behind the boat made things difficult. When fish die slowly, says Gast, their scales stick up at angles. But she didn't know this, and, with a policy of drawing exactly what she sees, she carefully limned the shadows cast by the scales.

But fish scales are supposed to be flat against the fish, and when the curator saw it, he said, "That's the most beautiful drawing of the worst fish I have ever seen in my life."

This fish is one of 80 of her illustrations now on display in the second floor rotunda balcony of Natural History. But it's the only one she terms "a disaster." The scientific illustrations hang near examples of medieval-type illuminations by Gast -- a sidelight that she plans to make into a career when she retires next year.

In the animal kingdom, the drawings include corals and crayfish, ostracods and isopods, slipper shrimp, lacebugs and marine worms. One of her drawings illustrates a new phylum -- the minute loricifera, which when magnified sometimes looks like a plant in a hanging basket. But remember when you look down on the silly loricifera that a phylum classification is so broad that mammals are merely a class in a phylum. This is only the third new phylum to be discovered this century.

This sort of illustration can't be trusted to free-hand. "My illustrations are meant to last forever, for use in comparative zoology," says Gast, "so they must be correct."

She does it through a complicated form of tracing -- using a stereo microscope that, through mirrors, projects the image of the illustrator's hand and drawing onto the slide.

Ordinarily, these illustrations appear only in scientific journals with limited distribution and titles like "Revision of Styraconyx (Tardigrada: Halechiniscidae)," or "The Crayfishes of Georgia."

But even for non-scientific types, they possess a certain beauty -- if you'll suspend judgment about, say, a squid's arm covered with hundreds of tiny suckers.

Gast has a theory about this special beauty. She says she can tell if her drawing is right, if it "looks right."

"That sounds kind of mystical, but there's an integrity to it," she says. "Because if it's ugly, chances are it's wrong. These little guys can't waste time with bad structure."

THIRTY YEARS OF SCIENTIFIC ILLUSTRATIONS DRAWN IN THE MUSEUM OF NATURAL HISTORY -- In the second floor rotunda balcony of the Museum of Natural History, through November 4.