80 



COELEXTERATA CNIDARIA 



SUB-BRANCH II 



flattened on one side ; external surface corrugated, and sending off hollow, 

 root -like exothecal processes. Calice marked with septal striae ; internal 



FIG. 126. 



Cystiphyllum cylindricum, Lonsd. Silurian; Iron Bridge, 

 England. ^4, B, Transverse and longitudinal sections (after 

 Nicholson). 



FIG. 127. 



Strephodes Murchisoni, Lons. 

 Showing strongly developed 

 dissepiments and tabulae. 



structure consisting of vesicular tissue and stereoplasma. Operculum in form 



of semicircular plate ; inner sur- 

 face traversed by median ridge 

 and fainter, granulated, parallel 

 elevations. Silurian. 



Calceola, Lam. (Fig. 129). 

 Corallum simple, semi -turbin ate. 

 or slipper-shaped, with one side 

 flat and triangular. Calice very 

 deep, extending nearly to apex, 

 and marked internally with fine 

 septal striae. Cardinal septum 

 placed in the centre of the vaulted 

 side, counter septum in middle of 

 flattened side, and alar septa at 

 the angles. Internal structure 

 composed of fine vesicular tissue 

 and stereoplasma. Operculum 

 semicircular, very thick, under 



Calceola sandalina, Lam. , " . 



Devonian; Eifei. Natural surface marked with prominent 

 median and fainter lateral septal 

 ridges. C. sandalina, Lam. Very common in Middle Devonian of Europe, 

 rare in Carboniferous Limestone of Belgium. 



FIG. 128. 



finii inpii /ill a at, pyramid' 

 ate, His. S p. Silurian; 

 Gottland. A, Specimen 

 with operculum. B, Calice 

 seen from above. Natural 

 size (after Lindstrom). 



FIG. 129. 



Range and Distribution of the Tetracoralla. 



The typical Tetracoralla are confined to the Palaeozoic rpfiks. They are 

 unknown in the Cambrian, and make their first appearance in the Ordovician, 

 where they are sparsely represented in North America and in Hfrope. Here 

 the most abundantly distributed genus is Streptelasma ; Cyathophyllum and 

 Ptychqphyttum being of rarer occurrence. The period of maximum development 

 falls in the Silurian, which contains the largest number of genera and species. 

 There are limestones found on the islands of Gottland and Dago (Esthonia), as 

 well as at Dudley, Shropshire, and at Lockport, New York, and other places in 

 North America, which are made up of ancient coral-reefs. The principal agents 



