PSEUDAXONIA. 327 



Sub-order III. Pennatulacea. — Free-living Alcyonarians consist- 

 ing of a stem and polypiferous branches. The colony is polymorphic. 



Family 8. Pennatulidae, . . . Pennaiula, Veretillum, &°c. 



So far as the sub-orders are concerned, the above classification is 

 only partially available for pakeontological purposes, as based upon 

 characters which are not recognisable in fossil forms. There are, 

 moreover, certain extinct groups of corals (Ha/ysitidcs, Tetradiidce, 

 Chcetetidce, &c.) which we must provisionally place among the 

 Alcyonarians, but which cannot, with our present knowledge, be 

 included in any of the three sub-orders above mentioned. 



As regards the distribution in time of the Alcyonarians, the fami- 

 lies of the Haimeidcz, Cornularidce, Alcyonidts, and Tubiporidcz have 

 no fossil representatives, so far as is certainly known ; and only the 

 last mentioned of these requires further notice here. On the other 

 hand, the families of the Pseudaxo?iia, Gorgo?iidce, Pemiatulidce, and 

 Helioporidce are all sparingly represented by fossil types in the 

 Secondary and Tertiary deposits. The extinct family of the Helio- 

 litidce is mainly Palaeozoic, its earliest representatives appearing in 

 the Ordovician rocks. In addition to the preceding, there are the 

 four families of .the Halysitidtz, Tetradiidce, Chcetetidce, and Aulopor- 

 idce, the members of which are apparently exclusively Palaeozoic, but 

 the true relationships of which are more or less uncertain. Still 

 more uncertain is the systematic position of the extinct groups of 

 the Monticuliporidce. and Fistidiporidce, which will be here treated 

 of apart from the Alcyonaria. 



In the following brief account of the fossil Alcyonarians, only 

 those families will be considered which are known to have fossil 

 representatives ; but the family of the Tubiporidce also demands a 

 short notice, from its supposed relationship to Syringopora. 



PSEUDAXONIA. 



This group of the Alcyonarians comprises forms in which the 

 skeleton is composed of mesodermal spicules, the sclerobasic axis, 

 when present, not being secreted by a continuous epithelial layer. 

 The spicules are sometimes {Briareum) completely detached, though 

 even in this case they may form in part a tolerably well-defined axis. 

 On the other hand, in the well-known Red Coral ( Corallium rubrum) 

 there is a dense calcareous sclerobase which is composed of spicules 

 or sclerites embedded in and united by a nbro-crystalline calcareous 

 matrix (fig. 211). The sclerobasic axis of Corallium is unjointed 

 and is branched, and its surface exhibits longitudinal grooves which 

 lodged the larger ccenosarcal canals (fig. 124). In Melithcea and 

 Jfopsea, again, there is a sclerobasic axis, but this is jointed, and is com- 



