1881 .] 
157 
[Dawson. 
Mr. S. H. Scudder presented the following note : 
NOTE ON SPIRORBIS CONTAINED IN AN IRONSTONE 
NODULE FROM MAZON CREEK, WITH MILLIPEDE. 
BY J. W. DAWSON. 
The shell pointed out by Mr. Scudder as occurring in the same 
' nodule with Acantherpestes major, 1 is minute and discoidal, 
not enlarging rapidly, dextral, and with about two volutions. 
The external surface can be seen only in a small part of the shell. 
It is marked with strong transverse irregular ridges, on which are 
finer irregular transverse lines or striae. It is not distinguishable 
either in form or markings from specimens of Spirorbis in my col- 
lection from the coal formation of Nova Scotia. These I refer to 
S. (Microconchus) carbonarius 2 which is common to America and 
Europe, and the present specimen may be referable to the same 
species, which is very variable in its markings; but a single 
specimen, and this so imperfect, is not sufficient to render this 
determination certain. 
The shell does not seem to have been attached to the Millipede, 
but to have been loose. This is however a very common mode of 
occurrence with Spirorbis carbonarius, which was frequently at- 
tached to submerged plants and on their decay was set free. 
This little Spirorbis is so very plentiful in beds containing terres. 
trial remains, that there is nothing singular in its having been 
drifted between the legs of a dead millipede. 
In the Report of the Geological Survey of Illinois, Vol. II, p. 
462, Lesquereux notices the occurrence of worm-shells referred 
by him to Spirorbis carbonarius on ferns and other plants at 
Colchester, Illinois. The figures which he gives (pi. 88, fig. 6) 
show a variety somewhat more rapidly expanding and more 
smooth than the present specimen. Professor Whitfield has 
recently described 3 another species, S. anthracosia, from the 
iSee Memoirs of the Society, Vol. in, Art. 5 (in press). 
2 S. ( Microconchus ) pusillus of Martin is not improbably the same, in which case his 
name has priority. 
3 American Journal of Science, Vol. xxi, No. 122. 
