53 
certain limits in its thickness, and so exceedingly regular in its development 
that it possesses every feature presented hy the layer of secondary sclcren- 
chyma ■which is deposited on the inside of the proper wall of Fcichjpora^ 
Laceripora, and other similar corals. 
This secondary deposit is invariably similar in every corallite of an 
individual speeimen, l)oth in charaeter and amount. In one specimen it may 
he of considerable width, and very dark in colour ; in another narrow and 
jiale, hut there is no commingling of the two kinds. The smallest intercalated 
tubes follow the same rule. It is carried to the greatest extent, throughout 
the suite of specimens examined hy me, in one from Singleton, Avherein the 
tubes are all hut choked up hy it, leaving only the smallest particle of clear 
crystalline calcite in the centre. The investing nature of this deposit cannot 
he better studied than in transverse sections (PI. Ill, Pig. 6), Avhcn it 
appears as a vertical crust completely lining the proper walls of eacli corallite. 
When S. crinita is devoid of this secondary deposit, the tube walls are very 
uniform in appearance, clear and distinct, forming a remarkably regular and 
constant network. Touching the nature of this deposit, the following is the 
conclusion of Prof . Nicholson and the Writer: — “ This curious investment, in 
sj)ite of its extraordinarily regular development, is of inorganic origin, and is 
produced hy a post-mortem deposition of carbonate of lime within the 
cavities of the tubes. We have been led to this conclusion principally hy 
twm considerations. In the first place, Ave found that in one specimen of 
S. crinita, as ahoAm described, this secondary lining of the tubes had no 
existence at all. In the second place, Ave found that in another specimen of 
the same species this singular brown lining w*as present, l)ut Avas irregnlar in 
its development, terminating in a ragged free edge wdiere it surrounded the 
Ausceral chamber.” ^ In PI. Ill, Pig. 6, this infilling investment is exceedingly 
Avell showm from a calcareous and naturally-Aveathcred specimen. On the 
upper left and towards the lower centre of the figure four corallites Avill ])e 
noticeable as nearly completely closed. 
Well-marked acanthopores are at times placed at the angles of junc- 
tion of the corallites, but their presence is by no means regular. They are 
sometimes minute, but at other times large, circular, thick- Availed, and showing 
a distinct lumen. In the tyj)e specimen in London they are plainly visible 
in all the sections made, but in a number of the specimens contained in our 
Collection their presence is uncertain, although at times they can be detected. 
1 Ann. Mag. Nat. Hist., 1886, XVII, p. 184. 
