. 32 



Plate IV. Fig. 16, is the representation of an elegant corallite, from 

 the chalk-pits, at Northfleet in Kent, attached to the chalk in which 

 it was found imbedded. Its root, which is adherent to a plate of an 

 echinus, is regularly indented with angular excavations, which appear 

 to be about eight in number. From the root proceeds the body of the 

 cora.1, gently bending and gradually enlarging into a conical form, 

 about an inch in length. Its under and external surface is elegantly 

 striated with distinct ridges, regularly disposed in the following order : 

 Midway between every two of the largest ridges is placed one rather 

 smaller. The star on the disk (a) is formed by perpendicular lamellae, 

 reaching from each of the largest ridges on the circumference, to the 

 centre, and by smaller lamellae proceeding from each of the ridges of 

 those of a smaller size, but which reach- a very little way towards 

 the centre. As there are no transverse ridges on the external surface, 

 so there are no horizontal plates observed internally, at least as low as 

 the eye can command, which is very near to the bottom. 



The specimen, Plate IV. Fig. 15, is also from the chalk-pits at 

 Northfleet. In this delicate specimen, the pedicle is very observable ; 

 the ridges, on the external surface, are all nearly similar in size, and 

 disposed with much regularity and neatness. The stellated disk (b) 

 is formed by perpendicular plates, answering to -each of these ridges, 

 and nearly meeting in the centre. 



The madreporite, Plate IV. Fig. 9> which I have reason to believe 

 to be an Italian fossil, is in the form of a flattened cone : at the point 

 of the cone appears to have been a pedicle, from which proceed 

 innumerable striae which terminate in the other end of the cone: where 

 a star is formed, which differs materially in its form from any which 

 have existed in the specimens hitherto mentioned. From the inner sides 

 of the cone proceed perpendicular plates which meet, not in a point in 

 the centre, but in a line, possessing about three-fourths of the centre 

 ,of the longest diameter of the base of the cone. 



