74 BRITISH STROMATOPOROIDS. 



Section A (" Hydractinioid " Group). 

 Fam. 1. ActtnostromiDjE, .ZV7c&. 



Skeleton composed of distinct radial pillars which give off horizontal processes, these latter having a 

 radiating arrangement, and inosculating with one another in such a manner as to give rise to a 

 ''rectilinear" meshwork. Radial pillars confined to the separate interlaminar spaces, or passing con- 

 tinuously through many successive laminae. Definite zooidal tubes are wanting, or are very imper- 

 fectly developed. 



Genera. — Actinostroma, Rich. ; Clathrodictyon, Nich. and Mur. ; Stylodictyon, Nich. and Mur. (?). 



Fam. 2. Labechiid^;, Nich. 



Ccenosteum usually laminar or massive, with a basal epitheca; sometimes cylindrical. Skeleton 

 composed of curved or horizontal calcareous plates, arranged so as to constitute a stratified vesicular 

 tissue, but not giving rise to concentric " laminae." Radial pillars sometimes well developed and 

 "continuous," at other times rudimentary. Definite zooidal tubes not developed. 



Genera. — Labechia, E. and H. ; JRosenella, Nich. ; Beatricea, Bill. (?) ; Dictyostroma, Nich. (?). 



Section B (" Milleporoid " Group). 

 Fam. 3. Steomatopoeid^;, Nich. 



Ccenosteum having the radial and horizontal elements so combined with one another as to give rise 

 to a more or less continuously reticulated skeleton. Skeleton-fibre minutely porous or tubulated. 

 Definite zooidal tubes furnished with " tabulae " are developed. 



Genera. — Stromatopora, Goldf. ; Stromatoporella,W\c\i.; Parallelopora, Barg. (sub-genus?); Syringo- 

 stroma, Nich. (sub-genus?). 



Fam. 4. Idiosteomid^:, Nich. 



Ccenosteum usually cylindrical, often branched and dendroid, with a principal "axial tube," 

 which is intersected by tabulae and gives off lateral tabulate branches. Definite zooidal tubes are 

 present. The general tissue of the skeleton is continuously reticulated, and the skeleton-fibre is 

 mostly porous or tubulated. 



Genera.— Idiostroma, "Winch. ; Hermatostroma, Nich. Amphipora, Schulz ; Stachyodes, Barg. 



