Antipathes. 4. Melitxa.
This extensive order comprehends most of the large and elegant tropical species of the calcareous zoophytes, whose vast operations in the seas of the southern hemisphere are so well calculated to ex cite our admiration, and to interest the attention of the navigator. They have a calcareous axis, often of great density, and marked on the surface with radiated, stellular, or undulated impressions formed by thin elevated lamella. In the recent state the whole body is covered with a soft gela tinous flesh, in which the polypi are lodged. The gemmules are formed in clusters at the base of each polypus, and pass out through these organs. The genera of this order are, 1. Oculina. 7. Explanaria. 13. Fungia.
2. Seriatopora. 8. Echinopora. 14. Cyclolites.
3. Madrepora. 9. NIonticularia. 15. Turbinolia.
4. Pocillopora. 10. Meandrina. 16. Caryophyllia.
5. Porites. 11. Agaricia. 17. Sarcinula.
6. Astrea. 12. Pavonia. 18. Stylina.
In the zoophytes of this group the tubular per forations or cells for lodging the polypi arc not formed by delicate radiating lamella, as in the preceding order. They have a compact calcareous axis, sometimes beautifully coloured, and the polypi have a complicated structure. The greater num ber of the zoophytes of this order are fossil. The genera are, 1. Tubipora. 4. Millepora. 7. Lunulites.
2. Catenipora. 5. Distichopora. 8. Ovulites.
3. Favosites. 6. Orbulites.
The axis of the zoophytes, belonging to this group, is composed of delicate calcareous expan sions generally cellular or reticulated, and never forms compact masses as in some of the preceding orders. The surface is composed of minute shal low cells, arranged for the most part in regular series, for the lodgment of the polypi, and for the formation of the gemmules. The polypi have generally very numerous tentacula furnished with vibratory cilia. The polypi and gemmules appear, from observations made on several species of the Frith of Forth, to succeed each other alternately in the same cells, and in those which have been examined the gemmules are irritable, and have cilia on their surface, by which they move freely to and fro after their separation. The calcareous
zoophytes most common in our northern latitudes belong to this order. The genera are, I. Dactylopora. 5. Adeona. 9. Tubulipora.
2. Ocellaria. 6. Eschara. 10. Flustra.
3. Alveolites. 7. Cellepora.
4. Retepora. 8. Discopora.
The zoophytes of this order have seldom a cal careous axis. The axis, composed generally of a horny substance, forms tubular cells or sheaths for containing the polypi. They are fixed animals, generally ramified, and the horny axis is placed on the surface. The tentacula of the polypi are very numerous, and are generally furnished with vibra tory cilia. This order comprehends almost all the flexible horny zoophytes, so numerous in spe cies in every sea, and so much distinguished for their delicate plant-like ramifications. They have generally also a ramified base like a root. The gemmules are produced in vesicles which extend from the surface, and which fall off when the gem mules have escaped. The gemmules are at first connected by filaments like umbilical cords, with the fleshy matter contained within the horny axis. The genera of this order are, I. Polyphysa. 6. Cellaria. 11. Sertularia.
2. Acetabulum. 7. Liriozoa. 12. Campanularia.
3. Tibiana. 8. Serialaria. 13. Cornularia.
4. Dichotomaria. 9. Plumularia. 14. Tubularia.
5. Anguinaria. 10. Antennularia.
This order comprehends a few fresh water ge nera grouped together more by their abode than their organization. Three of the genera are fixed zoophytes, and the other two more freely to and fro. They are found encrusting stones and other objects on the margin of fresh water lakes. They form irregular masses perforated on the surface by the cells of the polypi, or by canals which traverse their whole interior. The polypi have an incom plete circle of tentacula around the mouth. In the Spongilla there are pores and internal canals with out polypi. The genera of this order are, I. PlumateIla. 3. Spongilla. 5. Difflugia.