140 
G. W. Lee — Trepostomata. 
II. —Morphology and Systematic Position. 
Class B r y o z o a Ehrenberg. 
Order Q-ymnolaemata Allman. 
Sub-Order Trepostomata Ulrich. 
Definition. —The above classification was proposed by Ulrich 1 in 1882, and is now 
almost universally recognised, there being at present but few upholders of the former 
view that the branching, massive or encrusting colonies typified by Monticulipora were 
Tabulate Corals 2 allied to the Favositidae or the Chaetetinae. 
The distinguishing character of the Trepostomata is that the zoarium or colony 
is composed of fasciculated tubes—the zooecia —which in their proximal portion are thin- 
walled and prismatic, while near the end of their course they change in character and 
direction, becoming thick-walled and bending outwards. The zoarium—when ramose— 
is thus divisible into two regions : an axial region comprising the proximal ends of the 
zooecia, and a peripheral region comprising their distal ends. The axial and peripheral 
regions are also known respectively as “immature” and “mature”; these last-named 
terms are probably not quite appropriate, but, until better ones are suggested, are of use 
Avhen dealing with laminar or other irregular zoaria whose shapes would be incompatible 
with the use of the term “ axial.” 
In the majority of species the * zooecia are crossed by transverse partitions known as 
diaphragms or tabuloe , whose nature and arrangements have considerable classificatory 
value. 
In a number of genera small differentiated cells—known as mesopores —occur 
between the zooecia proper. They differ from the zooecia proper not only in size but 
also in being more or less angular, with a difference in the nature of the tabulation,, 
which is generally closer. 
The acanthopores are blunt spines projecting above the general surface. In 
tangential sections— i.e., shallow sections cut parallel to the surface—they appear as 
circular spots darker than the general tissue, and often showing a small central lumen. 
Since the mesopores and acanthopores were presumably occupied by specially 
modified polvpides, it follows that a colony in which they occur is composed of more 
than one kind of element, and is therefore heteromorphic. 
The monticules are small elevated areas composed of zooecia larger than the average. 
The maculae are small depressed areas made up of cells Smaller than the average. 
41, p. 149. 
2 51a, p. 114. 
