NOTES ON CYCLOCTSTOIDES 
25 
showed a system of radiating channels, two or three to a plate 
according to the size of the plate. This is one of the really im- 
portant specimens, and will be mentioned again. 
(9.) Cyclocystoides niUdus , Faber, is another of these so-called 
species, based on plates of the sub-marginal ring alone. It was 
found in the upper strata at Cincinnati. 
(10.) Cyclocystoides huronensis , Billings, from the “Hudson 
River,” at E,abbit island, Lake Huron, is based upon an interest- 
ing specimen, but was very inadequately described. It is dis- 
cussed again on a later page. 
Although 12 species have been described, the only specific 
differences so far pointed out are in the number of plates in the 
sub-marginal ring, all other supposed differences being in fact 
imperfections of the specimens. After handling a considerable 
number of specimens, the writer is still unable to point out any- 
thing on which specific descriptions can be based. Probably 
nothing satisfactory in that line will be accomplished until a 
large number of well preserved specimens have been collected. 
Of the specimens mentioned above, the types of Billings’ Cyclo- 
cystoides halli are important as showing the structure of the sub- 
marginal ring; C. salteri , Hall, C. magnus, Miller and Dyer, and 
C. huronensis , Billings, show the upper side of the disk more or 
less perfectly, and I am now able to present illustrations of two 
more very good specimens, one showing the upper side of the 
disk in a very satisfactory manner, and one showing the opposite 
side very well. 
Cyclocystoides halli, Billings. 
Plate III, figs. 1, 3, and 4. 
Cyclocystoides halli , Billings, 1858. Canadian Organic Re- 
mains, Decade 3, p. 86, pi. x bis, figures 1-7. 
The best of the specimens which served as the types of this 
species is that illustrated in figs. 2 and 3 of Billings’ plate x bis. 
This specimen is of especial value, as it shows the character of 
the plates of the sub-marginal ring, which are better preserved 
than on any other known specimen. The ring in this specimen 
