﻿20 MADREPORARIA. 



SYSTEMATIC AEKANGEMENT OF THE SPECIES. 



Gtoup I.— GLABROUS. 

 a. Exj^lanate. 



1. Montipora exigua. (PI. XXXI. fig. 1.) 



Description. — Corallum thin (1 mm.), explknate, spreading in small patches either en- 

 crusting or arching freely over previous growths or over other corals, helping with other 

 explanate Montiporans to build up a tliick loosely laminated crust (cf. 31. holsii). An epitheca 

 closely accompanies the growing edge. 



Calicles visible as faint specks, "3 to 0"5 mm. in diameter, about 1 mm. apart. In 

 younger, thinner portions with tliin, prominent, but very irregularly developed septa, parts of 

 two 'Cycles ; but in the older, thicker portions, the septa become stouter, one (directive) being 

 much thicker and coarser than the rest. The fossa is inconspicuous. 



The ccenenchyma- consists of a flaky reticulum, the fine points from the edges of the 

 flakes forming septa, in the younger specimens. In these, also, a flaky reticulum forms the 

 upper surface : it may be said generally that the flakes lie horizontally, but their edges are 

 turned up at all angles. In the older portions, the flaky reticular layer, of which the younger 

 stocks entirely consist, sends up. longer and thicker points. These, rising above the surface, 

 form, with the flaky reticulum, a coarsely granular porous- surface. 



There are two specimens. One (a) consists of two small patches forming part of a lami- 

 nated! crust mainl}'' composed of dead leaves of M. holsii (see p. 34). The other specimen (p) 

 is the minute young stock described in the Introduction, p. 7, and' figured' on pi. ii. vol. xx. 

 of the Anni and Mag. Nat. Hist. This was picked off the same mass of dead crust to which 

 specimen a still adheres. There is no actual proof that these three stocks belong to one 

 another. The two larger patches appear to be joined by dead coral in a- way which makes it 

 difiicult to doubt their being the same, while the differences between them seem to show that 

 the smaller may well be a transition form between the larger and the minute stock described 

 in the Introduction. The chief change seems to be that the flaky reticulum which in the 

 younger stages forms the whole ccenenchyma, becomes covered in the older specimens- 

 with a layer which is coarsely granular at the surface, as. shown in PL XXXL. None of the 

 specimens show sections. 



a. Billiton, on dead M. Bolsii. (Part of), 83. 7. 24 lfl3. (Type.), 



h. Minute young stage, Eilliton. 



