_Stromatopora_ is common in Devonian and also occurs in Silurian strata. _Cannopora_ from the Devonian has well-marked tabulate pores, and is often found associated commensally with another coral (_Aulopora_ or _Syringopora_). ORDER VI. STYLASTERINA. The genera included in this order resemble _Millepora_ in producing a massive calcareous skeleton, and in showing a consistent dimorphism of the zooids, but in many respects they exhibit great divergence from the characters of the Milleporina. The colony is arborescent in growth, the branches arising frequently only in one plane, forming a flabellum. The calcareous skeleton is perforated to a considerable depth by the gastrozooids, dactylozooids, and nutritive canals, and the {284}gastropores and dactylopores are not provided with tabulae except in the genera _Pliobothrus_ and _Sporadopora_. The character which gives the order its name is a conical, sometimes torch-like projection at the base of the gastropore, called the "style," which carries a fold of the ectoderm and endoderm layers of the body-wall, and may serve to increase the absorptive surface of the digestive cavity. In some genera a style is also present in the dactylopore, in which case it serves as an additional surface for the attachment of the retractor muscles. The pores are scattered on all aspects of the coral in the genera _Sporadopora_, _Errina_, and _Pliobothrus_; in _Spinipora_ and _Steganopora_ the scattered dactylopores are situated at the extremities of tubular spines which project from the general surface of the coral, the gastropores being situated irregularly between the spines. In _Phalangopora_ the pores are arranged in regular longitudinal lines, and in _Distichopora_ they are mainly in rows on the edges of the flattened branches, a single row of gastropores being flanked by a single row of dactylopores on each side. In the remaining genera the pores are arranged in definite cycles, which are frequently separated from one another by considerable intervals, and have, particularly in the dried skeleton, a certain resemblance to the calices of some of the Zoantharian corals. In _Cryptohelia_ the cycles are covered by a lid-like projection from the neighbouring coenenchym (Fig. 136, _l_ 1, _l_ 2). The gastrozooids are short, and are usually provided with a variable number of small capitate tentacles. The dactylozooids are filiform and devoid of tentacles, the endoderm of their axes being solid and scalariform.