130 



The GoEGONiD^ are characterised by their shrub-Hke ramose 

 Polypary, which is a central stem produced by an epidermic 

 sclerenchyma fixed to submarine bodies and consisting of a 

 horny axis for supporting the common tissue of the associated 

 Polypi. This family includes Goegonia, which belongs only 

 to our modern seas ; Isis, found fossil in the Upper Chalk and 

 Miocene, and living; Corallitjm (Red Coral) in the Upper Chalky 

 Miocene, and Uving. 



The PENNATTJLiDiE form free floating colonies of Polyps, 

 aggregated upon a common hollow pedicle; containing in general 

 a soUd styliform axis, and having a free caenosarc. 



The Geaptolithid^ have a solid horny axis often striated 

 longitudinally, and prolonged into the lines of the cellules. 

 Sometimes the axis is straight, or coiled into a spiral, either 

 wholly or in part ; or it forms a helix. After much difference 

 of opinion as to their true position, these remarkable fossils are 

 now considered to form a family of the Alctonaeia. 



They are all special to the Silurian period, and date among 

 the first animal forms of the old Lower Silurian deposits, 

 extending upwards into their upper strata ; but none are found 

 in rocks of more recent formation. 



M, DE Peomentel* divides the class Coealliaeia into two 

 sub-classes — 



disposed in a crown, tubular, and ") o i^ i 



^ communicating with the visceral ; „ 



Cokalliaria I Cnidairia. 



chambers. J 



having T p . , , 



fasciculated, non-tubular, and not \ 

 tentacula . . .,, ,, . ,1 Sub-class 



communicatmg with the visceral > 

 , , \ Podactinairia. 



chambers. / 



The anatomical disposition of the tentacula serves still farther 

 to enable us to sub-divide the Cnidaieia into two orders, 

 according as their number is fixed or variable, or as they are 



* Pal^ontologie Fraii9aise Ter. Cr6tac6 Zoophytes, torn. viii.. p. 155., 1863. 



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