PLATE 23. 



Fig. 1, 2, 3. 101. 2. Chjetetes lycopebdon. (Pag- 64.) 



1. Portion of a vertical section of a hemispherical form of large size, showing the radiating structure from 



increase of tubes by subdivision, and also the increase by development of marginal tubes. The tubes are 

 filled, and have become solid columns, which are easily separable by a slight blow of the hammer, 



I a. A portion magnified, showing only the enlarged columns ; the diaphragms not visible. 



1 b. Transverse section of a small conical or hemispheric form, showing the radiating arrangement of the tubes. 



1 c. A portion of the same enlarged, showing the diaphragms at regular intervals in some of the tubes which 

 are divided longitudinally. 



1 rf. Iff- Different external forms of the coral : 1 d and /, with more depressed forms, being the more usual ; 

 while 1 e shows a tendency to branching, which, if continued, would produce a coral with a massive 

 centre and numerous branches. 



I X. A large irregular mass with numerous diverging branches, some of which are broken off, showing the 

 radiating arrangement of the tubes from a central axis. This specimen exhibits the same tendency as in 

 1 e, carried forward to a greater extent, showing how the same form may produce the ramose varieties. 



1 A. A fragment from a larger mass, where the tubes are not filled with calcareous matter, showing the re- 

 gularity of the diaphragms, which are distant a little less than the width of the tubes. 



1 i. The same enlarged. The mass is light and spongy like recent coral, and appears to he composed of nu- 



merous smaller ones which were drifted together, and afterwards recommenced their growth, forming a 

 very irregular mass. 



2. var. ramottu. A fragment of limestone, with numerous worn fragments of a coral upon its surface. The 



structure of this coral is apparently identical with those just noticed, though it has assumed a perfectly 

 ramose form. 



2 a. A fragment enlarged, showing the columnar structure upon the worn surface. The tubes terminate at un- 



equal heights, from having been worn and broken ofi" in this manner. 



3. A cylindrical specimen having the bases of three branches above, which appear to have been suddenly 



contracted and discontinued ; as also the central shaft, which has been broken off, and partially healed 

 before the death of the animal. The form of the openings of the tube is not correctly given in this figure. 

 It is not unusual, in the branching forms, to find specimens in which the branches have been broken ofl"; 

 and the polyps adjoining the fracture, by the addition of lateral tubes, commence covering up the part, 

 and terminate it abruptly, as the branches of this specimen and the upper branches of 1 g. 



Fig. 4. 103. 4. ChjEtetes columnaeis. ( Pag. 68.) 



4. A fragment of the natural size. 4 a. An enlarged portion, showing the general form of the tubes. 



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