21 



are imbedded. In some, it is composed chiefly of brown argillaceous 

 matter ; in others, it is a pretty solid lime-stone ; whilst, in others, it 

 is formed of very fine particles of both argillaceous and calcareous 

 earth. The coral itself often varies in its colour and hardness. In 

 some specimens it is of a yellowish hue, and in others of a bluish 

 white. In some it is much harder and firmer than the investing matrix, 

 whilst, in others, possessing a spathose texture, it is much more fragile. 

 This coral is generally opaque and white ; but sometimes it has suffi- 

 cient transparency, to allow the transmission of the light through a 

 thin section of the mass, so as to render the parts of the coral visible, 

 as is shewn, Plate III. Fig. 6. 



In the specimen, Plate II. Fig. 3, the tubular folds reach sufficiently 

 above the matrix to afford a fair view of their structure. The grooves 

 formed on the external surface, between the prominences occasioned 

 by the tubes, are very plainly to be observed. Slight horizontal lines 

 crossing the former may also be perceived : and with the aid of a 

 lens, these manifest the appearance of having been formed by regular 

 additions of fresh matter, applied by the inhabitants of the tubes, 

 during the several stages of their growth. Minute openings are also 

 observable in the sides of the tubes, by which, it is probable, that a 

 connection was preserved betwixt all the parts of the animal mass, 

 with which the tubes were filled. 



The specimen, Plate III. Fig. 5, very much resembles that which is 

 figured by Bromcll, and which he so properly describes as approach- 

 ing in its appearance to a reticular plexus of lymphatics. The white 

 coral, being contrasted by the dark ground, yields indeed a very beau- 

 tiful appearance, and gives also the idea of the laboured works of 

 some nice artist. 



Tubipora serpens, as appears from the figure and description given 

 by Fougt* of the fossil referred to under this head, can hardly be 



* Amcenit. Acad. Tom. I. p. 105, tab. 4, fig. XXVI. 



