The arthropods in general were provided with a carapace; most of them were crustaceans.
At least three segments of the trunk are left uncovered by the carapace.
The last four or five segments of the trunk are free from the carapace.
The Monosphrida comprise all those Sphroidea in which the carapace is represented only by one single lattice-shell.
In Chelonia the ribs are ...