PRESIDENTIAL ADDRESS. 457 
still swb judice and, while regarding it as probably an alga, we may venture 
to consider it more fittingly discussed among the Schizophyta than elsewhere.’ 
In 1908, however, Rothpletz, in discussing the relationship of Spherocodium 
and Girvanella, reaffirms his opinion that the latter must be referred to the 
Codiaceze.'? 
Mitcheldeania. 
This genus was first described by Mr. Edward Wethered from the Lower 
Carboniferous beds of the Forest of Dean’* under the name of Mitcheldeania 
Nicholsoni; it was referred by him to the Hydractinide, and considered to be 
allied to the Stromatoporoids. The figure accompanying this paper unfor- 
tunately fails to show any of the characters of the organism, but a better 
figure of the same species was subsequently published in the Proceedings of 
the Cotteswold Naturalists’ Field Club." 
In 1888 Prof. H. A. Nicholson ** published in the Geological Magazine figures 
and descriptions of a new species of this genus (J. gregaria), and redefined 
the genus as having ‘the form of small, rounded or oval calcareous masses 
made up of capillary tubes of an oval or circular shape, which radiate from 
a central point or points, and are intermixed with an interstitial tissue of 
very much more minute branching tubuli.’ He compares the larger tubes to 
zooidal tubes, and states that they ‘communicate with one another by means 
of large, irregularly-placed foramina resembling ‘‘the mural pores” of the 
Favositide, and they occasionally exhibit a few irregular transverse partitions 
or tubule.’ 
With regard to the systematic position of this genus, Nicholson remarks : 
“In spite of the extreme minuteness of its tissues, the genus Witcheldcania 
may, I think, be referred with tolerable certainty to the Celenterata .. . its 
closest affinities seem to be with the Hydrocorallines . . . on the other hand 
all the known hydrocorallines possess zooidal tubes which are enormously larger 
than those of Mitcheldeania; and there are other morphological features in 
the latter genus which would preclude its being actually placed, with our 
present knowledge, in the group of the Hydrocoralline.’ 
Since this description by Prof. Nicholson, no further account of this organism, 
so far as I am aware, has been published, and its reference to the Hydrozoa 
rests on Prof. Nicholson’s description. 
During the past few years I have collected a large amount of material 
from beth of the type localities from which Mr. Wethered and Prof. Nicholson 
obtained their specimens, and an examination of this material has impressed 
me strongly with the resemblance of Mitcheldcania to forms such as Solenopora 
and Girvanella, now usually classed among the Calcareous Algw. In the rocks 
in which it occurs Mitcheldeania appears as rounded and lobulate nodules, 
breaking with porcellanous fracture and showing concentric structure on 
weathered surfaces, very similar to nodules of Solenopora; while under the 
microscope the branching character of the tubules and their comparatively 
minute size appear to separate them from the Monticuliporoids. Prof. Nicholson 
appears to rely on the presence of pores, which he thought he observed in the 
walls of both the larger and finer tubes, for the inclusion of this genus with 
the Hydrocorallines, though he appeared to be doubtful about their occurrence 
in the interstitial tubuli. An examination of a large number of slides has 
failed to convince me of the presence of pores, even in the larger ‘ zooidal 
tubes.’ The large ‘oval or circular’ apertures noticed by Nicholson appear 
to be either elbows in the undulating tubes cut across where these bend away 
from the plane of the section, or places where a branch is given off from a 
tube at an angle to the plane of the section. If this view be accepted, there 
appears to be no sufficient reason why Mitcheldeania should not be ranged with 
Solenopora and other similar forms, and included among the Calcareous Algw— 
a position which its mode of occurrence and general structure has led me, for 
some time, to assign to this organism. 
In addition to the three chief forms described above from British rocks, a 
12 Op. cit. (8). 
13 Geol. Mag., Dec. III., Vol. IIT., p. 585, 1886. 
M Vol. IX., p. 77, pl. v., 1886. 
19 Op. cit. (4), p. 16. 
