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Any one of numerous species of extinct arthropods belonging to the order Trilobita. Trilobites were very common in the Silurian and Devonian periods, but became extinct at the close of the Paleozoic. So named from the three lobes usually seen on each segment.

A genus of trilobites found in the Lower Silurian formation. See Illust. in Append.

The anterior segment of the shell of trilobites.

A genus of trilobites characteristic of the Silurian age.

A genus of trilobites, of many species, common in the Upper Silurian and Devonian rocks.

(Paleon.) The reflexed margin of the trilobite carapace.

The median, convex lobe of the head of a trilobite. See Trilobite.

The lower lip of trilobites, crustaceans, etc.

A class of Arthropoda, allied to the Crustacea. It includes the trilobites, Eurypteroidea, and Limuloidea. All are extinct except the horseshoe crabs of the last group. See Limulus.

A genus of large trilobites characteristic of the primordial formations.

A genus of trilobites found in the Silurian and Devonian formations. Phacops bufo is one of the most common species.

The caudal plate of trilobites, crustacean, and certain insects. See Illust. of Limulus and Trilobite.

An extinct order of arthropods comprising the trilobites.

Of, pertaining to or containing, trilobites; as, trilobitic rocks.

A genus of Lower Silurian trilobites in which the glabella and cheeks form three rounded elevations on the head.