336 



CHARACTERS AND DIVISIONS OF ALCYONARIA. 



" coenenchymal gemmation." The structure of the skeleton is not 

 spicular. 



As regards the minute characters of the skeleton, the autopores 

 and siphonopores are thin-walled, and no traces of the peculiar pris- 

 matic rods of the corallum of Heliofiora can be detected. The 

 siphonopores are generally so largely developed as to form a com- 

 plete zone, of one or more rows, of small tubes between adjacent 

 autopores (fig. 216, b) ; but in Heliolites dubius (fig. 217, a) the 

 number of the siphonopores is much reduced, and contiguous auto- 

 pores are largely in contact. Both sets of tubes are furnished with 



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Fig. 217. — a, Cross-section of Heliolites dubius, from the Ordovician rocks of Esthonia, en- 

 larged ten times ; b, Vertical section of the same, similarly enlarged, showing the spiniform 

 septa; c, Tangential section of Heliolites porosus, from the Middle Devonian of Biichel, showing 

 "coenenchymal gemmation," enlarged ten times; d, Part of another cross-section of the same, 

 enlarged about twenty times, showing fission of the siphonopores. si, Siphonopores ; au, Auto- 

 pores ; an! ', Autopore being developed by "coenenchymal gemmation";/, Incomplete septum 

 in a siphonopore, indicating partially accomplished fission of the tube. (Original.) 



tabulae, which are more numerous in the siphonopores than in the 

 autopores (fig. 216, c). The siphonopores are without septa, but 

 the autopores possess septal ridges or spines, which are very variable 

 in their development, but are almost always twelve in number in 

 each autopore. In some species {Heliolites inters tinctus, H. Mur- 

 chisoni, &c.) the septa are lamellar, but are rudimentary, and may 

 even be represented only by slight bendings of the walls of the auto- 

 pores. In other species (If. porosus, H. parvistella, &c.) the septa 



