80 COELENTERATA—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 
Z 
ae Ch ie 
i 2 

Fig. 126. Fic. 127. 
Cystiphyllum cylindricum, Lonsd. Silurian; Iron Bridge, Strephodes Murchisoni, Lons. 
England. 4A, b, Transverse and longitudinal sections (after Showing strongly. developed 
Nicholson). 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-turbinate, 
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. = Opereulum 

Goniophyllum pyramid- 
me, His. sp. Silurian ; Fic. 129 P 
Gottland. A, Specimen ; semicircular, very thick, under 
with operculuin. B, Calice Caleeola sandalina, Lam. a Mie . 
seen fromabove. Natural Devonian; Eifel. Natural surtace inarked with prominent 
size (after Lindstrom). size. : : 
median and fainter lateral septal 
ridges. C. sandalina, Lam. Very common in Middle Devonian of Europe, 
rare in Carboniferous Limestone of Belgium. 
Range and Distribution of the Tetracoralla. 
The typical Tetracoralla are confined to the Palaeozoic rocks. They are 
unknown in the Cambrian, and make their first appearance in the Ordovician, 
where they are sparsely represented in North America and in Europe. Here 
the most abundantly distributed genus is Streptelasma; Cyathophyllum and 
Ptychophyllum 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-veefs. The principal agents 
