20 
field ” Troedsson mentions (126) that there are more than twenty septa, 
which he says are slightly developed and mainly indicated by “ costae.” 
In two of the specimens similarly identified by Troedsson, examined by 
the writer, there are no more than twenty and the same number is supplied 
by a count in the only figure of Troedsson’s (figure 2a, Plate 37) in which 
it is possible to see all of them. 
The examples of C. borealis Whitfield Troedsson that the wTiter has 
sectioned and studied are 433 and 431 (M.M.K.). The latter is a portion 
of a radiating corallum. The internal diameter of corallites at the surface 
is 2*5 mm. (Compare with Troedsson ’s 3 to 4 mm. It is impossible to 
take a diameter in any other way.) In section this specimen presents a 
very singular appearance, w^hich is not mentioned by Troedsson (Plate 
II, figures la, b). It is of C. canadensis type, but the corallites are separ- 
ated by a very considerable thickness of loose tissue, some as much as the 
diameter of a corallite. The elements of this tissue have the appearance 
of the longitudinal septal ridges of C. canadensis, but they are disposed as 
columns not at the periphery of the corallite but in the “ wall,” which 
they form together. In section they are rather circular and small, or 
large and irregularly angular; usually they lie slightly distant from each 
other, but they may be in loose contact. This structure recalls more than 
anything else the appearance of certain of Lindstrom’s illustrations of 
bacular coenenchyme (Lindstrom 1899, Plate XII, figures 6 and 7) ; but 
the analogy cannot be pursued far since the elements in this case are dis- 
tinctly separate and not fused up as in Lindstrom’s examples. This 
structure can be regarded as a very great development of a tendency seen 
in some other examples of C. canadensis, that of complicating the corallite 
boundary by irregular growth of longitudinal supports probably akin to 
the septal ridges. If this conception is true, no new structure is developed, 
there is merely multiplication of existing structures. 
Since this is the only example of this structure that has come to the 
notice of the writer, it is perhaps safest to regard the specimen, for the 
present at any rate, as an individually developed C. canadensis, with which 
it agrees in all other respects. It will be noticed that the effect on the 
corallum is the same as in the case of the variation to var. anticostiensis, 
namely, a separation of calices. It is not without interest that such a 
form comes from the same locality and horizon as the forma arctica, 
another form that shows peculiar development. 
The other example of C. borealis Whitfield Troedsson (M.M.K. 433, 
prep. 101) is a smaller fragment in which the external and internal appear- 
ance is well seen. It does not differ at all from typical C. canadensis, nor 
are the intercorallite “ walls ” particularly thickened. 
For the various reasons given above the following interpretation is 
suggested for Troedsson’s figures; this might, of course, have to be modified 
on the inspection of the specimens themselves: Plate 33, figures 2a, b, C. 
canadensis; Plate 34, figure 1, probably var. ungava, figures 2 and 3 prob- 
ably C. canadensis; Plate 35, probably var. ungava; Plate 36, probably 
C. canadensis, the specimen is reminiscent of certain Akpatok Island 
examples; Plate 37, a large var. anticostiensis approaching forma arctica; 
