GENERA OF FAVOSITID^. 137 



tlonal, or as owing its apparently massive form merely to the 

 coalescence of a succession of crusts. 



The calices of C. linearis, E. and H., are very characteristic. 

 They appear as long linear slits (PI. VII., figs, i-i b), which 

 may be nearly straight, but are more commonly strongly curved, 

 and which have their margins toothed by a variable number of 

 septa (most generally two on one margin, and one on the other), 

 while they have the appearance of being embedded in a dense 

 compact ccenenchyma. The form of the calices accurately 

 expresses the form of the visceral chamber to a certain depth 

 (half a line to nearly one line) below the surface, and tangential 

 sections taken within this depth (PI. VII., fig. i c) show that 

 the tubes are still curved linear fissures, with denticulate mar- 

 gins, and surrounded by dense calcareous tissue. In the in- 

 terior of the corallum, on the other hand, the corallites appear 

 as thin-walled, subpolygonal, compressed tubes, with freely 

 open cavities. The internal structure, in fact, is precisely the 

 same as that already described as characterising C. juniper inus, 

 Eichw. Thus, sections taken at right angles to the flat surfaces 

 of the frond (PI. VII., fig. i d) show that the gently-diverging 

 and thin-walled tubes of the central area, on approaching a 

 point situated a line or less below the actual surface, suddenly 

 bend outwards, nearly at right angles to their former course. 

 They now dilate, but their central cavity, instead of under- 

 going a corresponding expansion, becomes now still further 

 restricted, and is reduced to a narrow linear chamber, which 

 occupies one side of the corallite, the whole of the remaining 

 space within the walls of the latter being occupied by a dense 

 secondary deposit of sclerenchyma. There is, however, no 

 true " ccenenchyma ; " and the appearance of such a structure 

 is only due to the deposition of this sclerenchyma in the 

 interior of the tubes, and its coalescence in contiguous coral- 

 lites, to the more or less complete obliteration of the walls of 

 the latter as recognisable structures. Lastly, sections taken 

 through the median plane of the frond, and parallel with its 



