66 PALAEONTOLOGY OF NEW-YORK. 



Fig. 2, var. ramosus. 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. Large surfaces of limestone, covered with such frag- 

 ments, are found in many situations where the hemispheric form does not occur, as well as 

 where that is found. 



Fig. 2 a. A fragment enlarged, showing the columnar structure upon the worn surface. The tubes 

 terminate at unequal heights, from having been worn and broken off in this manner. 



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

 suddenly contracted and discontinued ; as aiso the central shaft, which has been broken ofT, 

 and partially healed before the death of the animal. The form of the openings of the tube 

 is not corrccllv given in this figure. It is not unusual, in the branching forms, to find speci- 

 mens in which the branches have been broken off, 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. 



Numerous figures might be given, illustrating the varieties of form assumed by this coral. 



The following have been added on Plate XXIV. : * 



Fig. 1 a. Section of a small hemispherical mass, showing the tubes nearly vertical to the base. 



Fig. I i. A portion of the same magnified. 



Fig. 1 e. The base of one of the hemispherical forms, where the polyps have just commenced their 

 operations ; the tubes, though distinctly formed, have scarcely a perceptible elevation. The 

 polyps here commenced their operations by attaching themselves to a valve of the Orthis 

 testudinaria, and thence extended laterally on all sides. This is the common mode of com- 

 mencing their growth; and an examination of the base usually reveals the fragment of some 

 shell, trilobite, or other organic body in the centre. The tubes do not attach directly to this 

 foreign body, but a kind of membranaceous envelope is first spread over it, and from this the 

 tubes take their origin, the envelope continuing to extend laterally as the growth of the coral 

 advances. 



Fig. I d. A small membranous envelope of this coral, from which, in some parts, the tubes have just 

 commenced rising : this substance is thin, and concentrically wrinkled on both sides. These 

 bodies are often found of an inch or more in diameter when the tubes have scarcely com- 

 menced their growth ; and in many cases we find them not more than half a line in height, 

 and are thence able to trace them through all their stages of growth. 



Fi"^. 1 e. A portion of an irregular massive specimen, showing a tendency to branching more distinctly 

 than the specimens represented on Plate XXIII. 



Fig. 1 /. A few tubes of the same enlarged, showing the structure before exhibited in the hemispheric 

 masses. 



Fig. 1 g. A cylindrical branched specimen. 



Fig. 1 A. A portion enlarged, showing the radiated tubes. 



Fig. 1 t. Enlarged ends of the tubes on the surface of fig. 1 g. 



Figs. I m 6:- \ k. Smaller branched and cylindrical specimens. In these the direction of the tubes is 

 more nearly in the direction of the axis of the coral, as shown in fig. I o : they are, otherwise, 

 similar to the previously noticed forms. The opening of the tubes upon the surface being 

 likewise more oblique to the axis, they present a different form as represented in fig. 1 n. 

 It is possible that these small forms may be foimd constant enough to receive a distinct 

 designation ; but at present 1 perceive so insensible a gradation from these forms to figs. 1 g 

 and 1 e, that I am unable to define any limits to either variety. 



