328 



CHARACTERS AND DIVISIONS OF ALCYONARIA. 



posed alternately of soft and hard segments, the former being com- 

 posed of separate sclerites united by horny matter, while the latter 

 are made up of fused spicules. In Sclerogorgia, finally, there is an 

 unjointed axis, consisting of horn with embedded sclerites, while 

 there are also free spicules in the soft tissues. 



As regards the geological distribution of the Pseudaxonia, the 

 genus Corallium appears to be represented in rocks as ancient as 



Fig. 211. — Part of a longitudinal section of Corallium rubrum, magnified 180 times, showing 

 the spicules of the skeleton united by a crystalline or fibrous matrix, produced by the calcification 

 of the soft interspicular tissues. (Original.) 



the Jurassic, and the Eocene Tertiary has yielded the remains of 

 the genera Mopsea and Websteria, of which the former still survives, 

 while the latter is confined to the Eocene and is of uncertain 

 affinities. 



Tubiporid^e. 



This group of the Alcyonarians comprises only the recent genus 

 Tubiflora, including the familiar " Organ-pipe Corals." There is a 

 well-developed corallum in Tubifiora composed of numerous cylin- 

 drical tubes or thecse, separated by small intervals, and connected 

 with one another by horizontal calcareous floors, which form a series 

 of concentric laminae parallel with the upper surface of the colony. 

 These floors are produced by the coalescence of horizontal stolons 

 given out from the upper ends of the polypes, and new corallites are 

 budded out from their upper surface. Internally they are traversed 

 by horizontal canals which communicate with the visceral chambers 



