294 MR. W. D. LANG ON GROWTH-STAGES [ Mar. 2, 
In this specimen the Peduncle, Trochoid, and Cylindrical shape- 
stages are all long and pass gradually from one to another, giving 
the corallum a regularly tapering shape. A rejuvenescence very 
early in life makes a convenient demarcation between the Peduncle 
and Trochoid shape-stage. The Peduncle being smooth for the first 
quarter of its course, there is a Precostal stage (text-fig. 39, A). 
Low plain cost (text-fig. 39, B, costal-stage I.) succeed, and 
reach nearly to the first rejuvenescence ; but just before this the 
costze become higher (text-fig. 39, C’, costal-stage II.), and are 
almost ridged (text-fig. 39, D*, costal-stage III.) when reju- 
venescence occurs. On resumption of growth the coste are in 
costal-stage IT. (text-fig. 39, C*), but rapidly pass again to costal- 
stage ITT. (text-fig. 39, D’), which is the characteristic stage of 
the corallum as a whole, and continues to the distal side of 
the third rejuvenescence ; that is, at the second and third re- 
juvenescences the recapitulation is so Slight that costal-stage IT. 
is not repeated. At about halfway between the third and four th 
rejuvenescences there is a sharp katagenesis (text-fig. 39, E’), 
marked by a lowering of the costa and “the disappearance of the 
ridge. The cost then take on an etched ornamentation (text- 
fig. 39, F", costal-stage IV.), but are thrown back again to costal- 
stage ITT. (text-fig. 39, D*) after the fourth rejuvenescence. The 
katagenesis and advance to costal-stage TV. is again repeated 
(text-fig. 39, EH’, EF’), and then the corallum terminates. The 
Trochoid shape-stage passes insensibly into the Cylindrical between 
rejuvenescences two and three. 
2. PARASMILIA CENTRALIS (Mantell). (Text-fig. 40.) 
Madrepora centralis Mantell, 1822, “ Fossils of the South 
Downs,” pp. 159-160, pl. xvi. fig. 4. 
Type-specimen, B.M. no, 5462. 
On the expanded base of the type-specimen there is no appear- 
ance of costze (text-fig. 40, A). This Precostal stage is followed 
by very faint, low, plain coste on the Peduncle and lowest Trochoid 
shape-stages (text-fig. 40, B, costal-stage I.). By the mid- 
Trochoid shape-stage the cost, though still plain (or very faintly 
roughened), have become more prominent and higher (text- 
fig. 40, C, D, costal-stages II. & IIT.). They then undergo a rapid 
katagenesis and appear low again, but this time markedly etched 
(text-fig. 40, E, costal-stage [V.). Shortly before the first re- 
juvenescence the cost are heightened (text-fig. 40, EF’, costal- 
stage V.) and become ridged (text- fig. 40, G’, costal stage VI). 
Between the first and second rejuvenescences the shape passes 
from Trochoid to Cylindrical, and costal-stages V. and VI. are 
repeated (text-fig. 40, F’, G*); and though ‘there is no definite 
rejuvenescence after the second, alternations of costal-stages V. 
and VI. occur (text-fig. 40, F", G") and show periods of growth 
alternating with fleeting rest-periods. 
