72 McLean. — On the Fossil Genus Sporocarpon. 
Neither in the fossil Radiolaria nor in the Foraminifera is there any 
notable change of character between their earliest known forms and those 
of the present day. In the former case this covers nearly the whole period 
of the geological record, so that we may conclude that the Protozoa as 
a class are not only conservative of morphological character, but so 
fundamentally adaptable that the probability of any large group suffering- 
complete extinction is correspondingly reduced. It is suggested that in 
these fossils we are dealing with a highly specialized offshoot from a stock 
normally oceanic in habitat, which had become adapted to life in the vast 
swampy lagoons of the Coal Measures period, in water, that is to say, 
probably brackish, and certainly highly charged with organic matter. 
Under these conditions they underwent a change of nature, the originally 
mineralized skeleton becoming a chitinized structure, with a consequent 
degradation of rigidity, while the quiet waters appear to have favoured 
a higher elaboration of the extra-thecal cytoplasm than is to be found in 
related pelagic forms. Life in a less highly oxygenated medium would 
indeed render it obligatory. 
If these suggestions as to their origin from known forms of Protozoa 
be accepted as probable, it makes it easy to understand how liable they 
were to be extinguished when secular changes of level finally abolished the 
topographical conditions which had favoured them, and upon which they 
depended, as a parasite does upon its host, in a balance of adaptation. 
The former account, which has been already referred to, included the 
four genera which were provisionally united into the family Traquairidae ; 
namely Traqnairia , Sporocarpon , Oidospora , and Zygosporites , while a fifth 
genus, Calcisphaera , morphologically similar, but found in limestones and 
preserved in calcite, was briefly dealt with, as being probably confamiliar 
with the other forms. 
The first of these genera, Traqnairia , has already been the subject of 
a memoir by Mrs. D. H. Scott (3), who is collecting further information with 
a view to more comprehensive treatment on a future occasion. In regard 
to Zygosporites nothing can, so far, be usefully added to what has already 
been written about it, while Calcisphaera calls for a much wider range of 
investigation, not only in the Carboniferous Limestones, but also in rocks 
of similar character from other Palaeozoic formations, 1 before a satisfactory 
presentation of its nature can be made. From the casual notes of its 
occurrence made by various geologists it appears to be widely distributed 
both in space and time, and it may have played a large part as a rock- 
former in the older calcareous strata. While not clearly differentiated in 
many cases from fossil Radiolaria, or what are accepted as such by 
geologists, yet its calcareous preservation and some details of its 'organiza- 
tion appear to give it a claim to separate consideration as an organism 
1 Possibly in Mesozoic formations also, e. g. the grey shales of the Keuper marl. 
