The order contains only fifteen genera, but they are usually arranged in the following eight families:—
1. Lesueuriidae. Lesueuria.
2. Bolinidae. Bolina, Bolinopsis.
3. Deiopeidae. Deiopea.
4. Eurhamphaeidae. Eurhamphaea.
5. Eucharidae. Eucharis.
6. Mnemiidae. Mnemia, Mnemiopsis.
7. Calymmidae. Calymma.
8. Ocyroidae. Ocyroe.
Most of these Ctenophores occur in the warm and tropical seas; but Bolina is found occasionally at Plymouth in the month of May, on the west coast of Ireland, and at other stations on the British coasts. Eucharis is regarded as one of the most beautiful of the Phylum. A swarm, some miles in length, of large specimens of E. multicornis was met by the Plankton Expedition in the south equatorial current of the Atlantic during the month of September.