218 



RUGOSA AND ALCYONARIA. 



often many feet in length, of more or less cylindrical form, 

 and principally composed of a calcareous vesicular tissue, 

 essentially similar to that of Cystiphyl- 

 lum. In the centre is what appears to 

 represent a tabulate area, such as we 

 meet with in many of the Cyathophyllidce. 

 If truly corals, these huge fossils must 

 be regarded as very aberrant members 

 of the Cystipliyllidce ; but there is some 

 reason for thinking that Beatricea is per- 

 haps really founded upon peculiar forms 

 of Stromatoporoids. 



Fig. 113. Calceola san 

 alina. An operculate Ru- 

 gose Coral. Devonian. 



Fig. 114. Beatricea undulata. A, Diagram showing the internal structure as exhibited by 

 a longitudinal section ; B, Portion of the base of a specimen from the Hudson River forma- 

 tion (Lower Silurian), the real length of the portion figured being about two feet. (After 

 Billings.) 



ORDER III. ALCYONARIA. 



The Alcyonarian Zoophytes are Actinozoa in which the. 

 polypes possess eight tentacles, which are fringed on their sides 

 with lateral pinnce or papillce, hence the name of OctocoraUa 

 often applied to the order. Almost all the members of the 

 order are composite, the tubular polypes being united by a 

 ccenosarc, through which ramify canals by which their body- 

 cavities are placed in communication. 



Of the living groups of the Alcyonaria, the " Organ-pipe 

 Corals" (Tuliporidce) have a well -developed sclerodermic 



