122 Introduction to Animal Morphology. 



cylindrical papillae (Muricea). In Primnoa, the operculum 

 consists of three-pointed scales, and the axis consists of con- 

 centric, calcined, horny lamellae, surrounded by alternate, 

 non-spiculigerous rings of horny and crystalline calcareous 

 matter. 



2. Gorgonidoe coenenchyma smooth ; axis horny, some- 

 times flat, leaf-like, \vith anastomosing branches forming 

 small (Xiphigorgia) or large interstices, whose meshes are 

 cither open (Rhipidogorgia) or filled with soft coenenchyma. 

 In this case the sclerobase may be expanded into thin 

 lamella; (Phycogorgia) ; or round, with netted branches in 

 the leaf-like coenenchyma (Phyllogorgia*). In others, the 

 branches uiv tree-like, not anastomosing; and the zooids are 

 disposed either regularly on both sides of the coenosarc 

 (Pten .>r irregularly over its whole surface, which 

 may be fan-like or tasseled (Lophogorgia). The zooids are 

 cither sunk into the thick, corky (Plexaura), or skin-like 



>gorgia) cujnenchyma, or project on warts, with rounded 

 ni;i) or bila! Kunkva). Plexaurella has 



spicnles in laminae between layers of horny matter. Sclero- 

 gorgia has an uncalcitied, horny, spiculigerous axis. 



3. Gorgonellida,' axis rorneo-ralcareous, either straight, 

 unilaterally comb-like (Ctenocella), or rod-like (Juncella), in 

 structure like Plexaurella, but with spicules in the horny 

 laminae ; or branched, with (Vermicella) or without projecting 

 zooids (Gorgonella). In the last, the horny lamella? are con- 

 centric, calcified. 



Order 5. Isidaceae. The axis consists of alternate, 

 soft, and calcareous joints. 



This includes two families : Melithaeidae soft joints, 

 suberose, concentrically laminated ; hard joints made of 

 cemented spicules; branches arising sometimes from the 

 horny joints, which may be traversed by tubular canals 

 (Melithaea) ; Isididae hard joints of concentrically laminated, 

 calcined membrane, traversed by radial lamellae, but without 

 spicules ; soft joints horny, like the axis in Gorgonidae ; 



* Hymenogorgia differs in having free branches. 



