Observations upon Stenopora fibrosa^ etc. 371 



along the outer side of the walls is retained, the exposed surfaces 

 equally exhibiting the irregular lines of growth, and the absence of 

 fractured diaphragms. Care, however, must be taken in those species 

 which, like Favosites alveolaris, have the connecting foramina on the 

 angles, to detect the line of separation along that junction, as the 

 structural inequalities are there often great, and the dividing seams in 

 consequence concealed. . In some cases, also, an apparently perfect 

 blending is produced by a projecting foramen, being received within 

 a corresponding opposite cavity. In all these instances, nevertheless, 

 the exterior sides of the broad planes of the columns arer easily parted, 

 and their true nature may be clearly recognized. 



On the contrary, in Chetetes, the Avails of adjacent columns seem to 

 be inseparable, or formed of intimately united laminse. In extensive 

 sections of Chetetes radians, having the interior of the tubes but slightly 

 coated with infiltered matter, not a single instance was discovered of 

 the outer side of a wall. Many flat, vertical planes were noticed as 

 well as re-entering angles formed by the junction of two walls, situated 

 obliquely to the general surface of the specimen ; but in every case the 

 flat plane, or the re-entering angle, could be traced upward or down- 

 ward, till it passed within the area of a tube, and therefore ascer- 

 tained to be an inner portion of the same tube exposed by fracture ; 

 or, if this could not be eflfected, a careful examination of the edges of 

 the planes never failed to prove that they were rough, and that the 

 unevenness was due to the remains of walls which had projected from 

 them, and had constituted inner sides of destroyed columns. In other 

 specimens of the same species retaining the original substance of the 

 coral, but having the tubes filled with calcareous spar, not a vestige 

 of the outer surface of a wall could be discovered, and in others again, 

 in which the animal structure had been replaced by infiltered matter, 

 characters analogous to those of Favosites could in no wise be per- 

 ceived. 



These difierences are believed to be necessary results of the distinct 

 mode by which additional columns were developed in each genus. 



In Favosites, the additional tubes dependent on the growth of the 

 polypes originated, so far as the author is acquainted with the genus, 

 either in gemmules, deposited in interspaces, or developed on the ex- 

 treme margin of the parent polype. In either instance, a perfect 

 individuality immediately took place, and the young animal, which 

 rapidly attained considerable lateral dimensions, constructed its tube 

 without the area of the parent column, building up the walls unas- 

 sisted by its neighbors. In almost every example, the sides of the sur- 

 rounding tubes are impressed by those of the interposed tube, indicating 



