The carapace is the “shell” on the back of the crab. Many charactersistics of the carapace are used to distinguish between species. The length of the carapace is measured along the anterior-posterior axis, while the breadth/width of the carapace is usually measured from side-to-side. The breadth is measured between the tips of the antero-lateral angles, which is usually (although not always) the widest part of the carapace.
