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on the form of the corallites composing it, both autopores and mesopores, and 
appears to he one of the best of the minor macroscopic characters for specific 
distinction. The length of each chain depends naturally on the number of 
corallites composing it, and its outline on the degree of farcimenticity of the 
line of corallite openings. This sausage-string-likc outline is least marked in 
II. lithostrotonoides and II. australis, and very strongly so in H. pycnoblastoides , 
II. peristephiscus, and II. cralus. The more geometric the outline of a 
fcnestrule the shorter will be the chains bounding it, as in II. lithostrotonoides. 
As a general rule, the chains surrounding a fenestrule all originate from 
gonopores at the angles of the latter, but in some species, the chains not only 
do this, but also unite with one another in the centre of their straight courses, 
or in the case of a form possessing very labyrinthine fenestrules from the 
rolling side of the latter. 
7. Imperfect Chains. — It occasionally happens that a chain of corallites 
is incomplete, projecting into an already completed fenestrule, without 
attachment at its distal or outer end. This will be more fully treated of 
under Reproduction. 
8. Form and Structure of Corallites. — The corallites are cylindroidal, 
quadrangular, or polygonal, according to their position in a chain. As a rule, 
the cylindroidal are the largest tubes, and are termed autopores ; the polygonal 
are the medium in size, and the quadrangular the smallest, called by me the 
gonopores and mesopores respectively. It is customary to describe the 
corallum as consisting of corallites of two orders only— the “ normal corallites” 
of Nicholson, or “autopores” of Sardesson, 1 and the “interstitial tubes” 
of Nicholson, or “ tubules” of Lambe. I use the term autopore as Sardesson 
did, to imply the large cylindroidal corallites; and I borrow the term mesoporc 
for the smaller tubes in a chain, interpolated between the larger, first indicated 
by McCoy and Ilall, and subsequently by Lindstrom. I am farther of 
opinion that a third set of corallites exists, which I term gonopores. In 
general terms, it may be stated that all the corallites are long and tubular, 
and all the enclosing walls are imperforate. 
( a ) Autopores . — In the Australian species these are always the largest 
in the colony, and are invariably cylindroidal, placed end to end, when not 
separated by a mesopore in the chain line, or by a gonopore at the fenestrule 
angles. The autopores vary in outline to some extent — they may he oval, 
1 Sardesson, Neues Jahr. Min., Beil. -13d. V, Heft 2, p. 272. 
C 
