Clarkson, E. N. K. & Henry, J. L.: Structures coaptatives et enroulement chez quelques Trilobites ordoviciens et siluriens. [Coaptative structures and enrollment in some Ordovician and Silurian trilobites.]

Certain trilobites possessed highly adapted structures on the cephalon and pygidium, and sometimes also the thorar, which ensured very close interlocking of opposing surfaces during enrollment. Different kinds of structures are described in detail in selected Ordovician and Silurian genera. There is a simple ‘press-stud’ mechanism axially situated on the opposing cephalic and pygidial doublures of Kloucekia micheli, whereas in various species of Crozonaspis and in Kloucekia dujardini a projecting cephalic beak fits into an excavation under the caudal spine. The cephalic beak and corresponding pygidial excavation seemingly evolve towards a more pronounced form in successive species throughout time. Colpocoryphe rouaulti, by contrast, has a pygidial protuberance interlocking with a cephalic excavation. Complete specimens of Encrinurus tuberculatus and E. variolaris have very complex contact surfaces along opposing doublures, with various kinds of interlocking structures.