The top shell is a series of plates, each plate having concentric diamond-shaped rings on it. It is coloured grey to light brown to black (coloration will vary with sub-species); the bottom shell is yellowish to olive. The turtle has pale skin with black spots and wiggly marks on it.
Females grow larger than males, having an average shell size up to 7.5 inches (19 cm); the males have a shell size up to just 5 inches (12 1/2 cm.)
Various names are used to designate grading of Terrapin. “The standard length for those who buy and sell terrapin is six inches; when of this dimension they are called “counts” …… The small species of terrapin are divided into two classes: heifers, the under shell of these never measuring more than five inches in length, and bulls five to five and a half.”  You may also hear, confusingly, the terms “cows” used to refer to females, and “bulls” used to refer to males. Meat from females is more tender.
A female 6 to 8 inches (15 to 20 cm) in size will weigh about 2 3/4 pounds (1 1/4 kg.) A male around 5 inches (12 1/2 cm) will weigh about 3/4 pound (340g.)
One of the largest specimens noted was procured by Delmonico’s restaurant in December 1885. It was 8 3/4 inches (22 cm) long, weighed 9 1/2 pounds (4 1/3 kg), and had 56 eggs in it. 
Terrapin in warmer southern waters tend to grow larger than those in more northern, cooler waters.
The turtles eat clams, soft-shell crabs, snails, small fish and the occasional plant.
The females can start reproducing when they are between 8 and 13 years old. They make nests 6 inches (15 cm) deep in dunes along the shore in which they lay 4 to 18 pinkish-white eggs, which need 60 to 120 days before they hatch. The newborn are about 1 inch (2 1/2 cm) long.
In winter, the turtles hibernate a few inches below the surface of mud.
The meat, once extracted, can be cooked in a wine sauce. Some prefer a butter sauce, with wine, sherry or Madeira served in a glass on the side. Some prefer a cream sauce.
Any eggs found inside a Terrapin are considered a delicacy and are served with the meat, as is the liver.
Harvesting of the turtles is now severely restricted to prevent them from becoming an endangered species.
You scald a live terrapin in boiling water for around 2 minutes, then remove, and peel off the skin and toe-nails. Put into fresh boiling water, until the shell can be taken off easily and the leg meat is tender (45 minutes to an hour.) Take out of the water, remove lower shells and let cool. Clean, saving any eggs and the liver. (Rupturing the gall bladder will spoil all the meat.) Cut meat into pieces, and cook it in fresh water for another one to one and a half hours. The meat is now ready to be used in a recipe. Meat from smaller ones is more tender. Larger Terrapin can have some coarse meat in it that some say is best discarded.
(Complete directions can be found in Charles Ranhofer’s “The Epicurean, Part 1” which can be found on the Internet.)
Terrapin soup was very fashionable in the 1700 and 1800s.
Literature & Lore
Terrapin is the state reptile of Maryland, and the official mascot of the University of Maryland.
“The terrapin is the unchallenged star of Maryland’s cuisine, the diamond-back terrapin, not that inferior member with the golden stripe….. Even in Baltimore there are various schools of thought on the terrapin’s preparation for there is never just one way of preparing a ‘dish-of-dishes.’ There’s the ‘wine-in-sauce’ crowd. Even here is division for some insist on Madeira, some demand sherry. There’s the ‘purist’ school which makes the sauce of pure butter and serves the wine in the glass, to sip as you will. The purists claim any young diamond-back terrapin, that is the ‘cow’ of course, with her belly full of eggs, can stand firmly on her own legs without any assistance from wine. The wine adherents say no. It is their theory that terrapin has its very being in the wine. They admit that the flesh of the diamondback gives its substance, something for the teeth to touch, but the sherry gives the flavor. And in Philadelphia, had you heard, they put terrapin into a cream sauce. Tsch! tsch! That’s the Baltimoreans giving the idea the raspberry.” — Paddleford, Clementine (1898 – 1967). Food Flashes Column. Gourmet Magazine. March 1946.
“Terrapin” comes from the Algonquian Indian word “torope.”
In Britain, sometimes the word “Terrapin” is used to refer to any aquatic turtle.
 Ranhofer, Charles. Terrapin. The Epicurean, Part 1. New York: C. Ranhofer, 1894, page 423.
  Ibid., page 420.
DuBose Griffin, David Owens and J. Whitfield Gibbons. Diamondback Terrapin. Columbia, SC. SC Department of Natural Resources: Comprehensive Wildlife Conservation Strategy. 2005.
Lester, Lori A. Masters Thesis: Tracking terrapins through genetic analysis: Multilocus assignment tests shed light on origin of turtles sold in markets. Duke University: Nicholas School of the Environment and Earth Sciences. 2007.
Massachusetts Division of Fisheries & Wildlife. Diamond-Backed Terrapin. Westborough: MA. 2008.
Unknown. Hats off to the terrapin; and to the epicure who discovered and exploited it. New York Times. 12 March 1893. Page 17.