DE VEL OPMENT. 5 7 



that it is in its first origin a Ccrainopora. The smallest Ccranio- 

 porcB which I have hitherto seen consist of a thin circular disc 

 with elevated edges. From the smooth centre of the superior 

 surface four or five wedge-shaped zocecia radiate outwards, each 

 of a length of i-5th millim., their mouths being oblique, with 

 the inferior lip somewhat protracted. On both sides of the 

 mouth there is a short, pointed spine. In its interior such a 

 zocecium is transversely divided by some irregular tabulse. The 

 interstitial tubes which are so characteristic of the Discopoi^el- 

 lidcE are also distinctly seen between the zooecia of Ceramopora. 

 New zooecia are budded forth in quincunx from the corner of 

 the old zooecia, and in the periphery of the colony they become 

 more crowded, having the mouth oval and erected. In the 

 interstices is seen what might be taken for a coenenchyma ; but 

 this in reality is composed of nothing but smaller irregular 

 zocecia. When the colony has spread out laterally, there are 

 seen at the sides of the first smooth centrum several others 

 regularly distributed on the surface, from which zooecia radiate 

 just as if the disc were composed of an aggregation of coales- 

 cent initial buds. When the colony has thus gained the expanse 

 of an inch or more, the zooecia grow vertically upwards, and the 

 colony by-and-by assumes a semi-globular shape, and is con- 

 verted into a Montiatlipora. All the zooecia are then tubular, 

 their mouths quite circular, and armed with a pair of very short 

 spines, their size varying in different cases. The larger zooecia 

 have around them either an empty space, or, as above stated, 

 a cellular tissue resembling a coenenchyma, and consisting of 

 smaller circular or polygonal tubes. The walls of the zooecia 

 are solid, without any perforations, and interiorly quite smooth 

 and destitute of projecting ridges or septa. The tabulse are 

 very irregular in the large tubes, being oblique or deeply sunk 

 in the wall ; in the narrower tubes they are dense and regular. 

 The large zooecia are clustered in groups at tolerably regular 

 intervals, each group of six or eight members. In Upper 

 Silurian specimens they very seldom project above the surface, 

 and do not form the stranofe monticules which are so common 



