PENNATULID^E. 33 1 



ferable to the recent genera Primnoa and Gorgonella have also 

 been detected in the Miocene Tertiary rocks. 



Pennatulid^e. 



This family includes a number of Alcyonarians in which the 

 colony is not fixed to any foreign object, and is composed of a 

 central ccenosarcal stem or rachis carrying polypes superiorly, these 

 being commonly arranged on longer or shorter lateral branches. 

 The polypes are dimorphic, and the skeleton usually has the form 

 of an unbranched, horny or partially calcified sclerobase. This 

 group is also of small palaeontological importance, but the genus 

 Pavonaria has been recognised in deposits of late Cretaceous age, 

 and the remains of Graphularia have been found in the Eocene 

 and Miocene Tertiary. 



Helioporim:. 



This family, as here defined, comprises only the single genus 

 Heliopora, in which there is a well-developed sclerodermic corallum 

 (fig. 214, a) composed of tabulate tubes of two sizes, the larger of 

 these being furnished with radiating pseudosepta, which do not 

 correspond in number with the mesenteries of the living polypes. 

 The larger tubes of the colony ("autopores") have usually been 

 regarded as the true corallites, and the smaller interstitial tubes 

 (" siphonopores ") have been commonly considered as constituting a 

 " ccenenchyma " ; but the researches of Moseley on the living 

 Heliopora cczrulea have rendered it probable that the colony is really 

 dimorphic, the sexual zooids occupying the large tubes, while the 

 small tubes lodge imperfect sexless zooids. The large tubes or 

 " autopores " are crossed by well-developed horizontal " tabulae," 

 and are completely separated from one another by the smaller tubes 

 or "siphonopores," which are also tabulate (fig. 214, c). Apart 

 from their larger size, the autopores are further distinguished by the 

 fact that they exhibit internally a variable number of longitudinal 

 ridges which resemble the radiating " septa " of the Zoantharian 

 corals. In the living Heliopora ccerulea there are usually twelve of 

 these radiating ridges in each autopore, but they can hardly be said 

 to have any existence as definite structures, and appear rather to be 

 formed by the projection into the cavity of the autopore of the 

 prismatic siphonopores which bound the latter. In H Partschii, 

 of the Cretaceous rocks, the autopores possess from twenty-five to 

 twenty-eight radial ridges which extend inwards to some distance, 

 while H macrosto?na, of the same formation, has numerous septal 

 ridges, but these are shorter. In any case these septal ridges not 



