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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 median elevation behind the mouth in the arthropods.

An order of curious parasitic worms found on crinoids. The body is short and disklike, with four pairs of suckers and five pairs of hook-bearing parapodia on the under side.

Having toothlike mandibles; -- applied to certain insects.

One of the divisions of Flagellata, including the monads and allied forms.

Same as Peristome.

Same as Plagiostomous.

An order of Bryozoa of which Rhabdopleura is the type. See Rhabdopleura.

A division of trematode worms having more two suckers. Called also Polystomea and Polystoma.

A group of cells resembling a stoma, but without any true aperture among them.

A suborder of Medusæ which includes very large species without marginal tentacles, but having large mouth lobes closely united at the edges. See Illust. in Appendix.

The young attached larva of Discophora in the stage when it resembles a hydroid, or actinian.

cophora having large free mouth lobes. It includes Aurelia, and Pelagia. Called also Semeostoma. See Illustr. under Discophora, and Medusa.

An artificial division of gastropods including those that have siphonostomatous shells.

Pertaining to the Siphonostomata.

A division of dipterous insects in which the proboscis is large and contains lancelike mandibles and maxillæ. The horseflies and robber flies are examples.

An order of tailed aquatic amphibians, including Siren and Pseudobranchus. They have anterior legs only, are eel-like in form, and have no teeth except a small patch on the palate. The external gills are persistent through life.

Any one of numerous species of trematode worms belonging to Tristoma and allied genera having a large posterior sucker and two small anterior ones. They usually have broad, thin, and disklike bodies, and are parasite on the gills and skin of fishes.

Not customable, or subject to custom duties.

pelvis. Also, the cavity of the belly, which is lined by the peritoneum, and contains the stomach, bowels, and other viscera. In man, often restricted to the part between the diaphragm and the commencement of the pelvis, the remainder being called the pelvic cavity.