TOO 
SMITHSONIAN INSTITUTION 
in width of brachials, length and stoutness of ramules, and where observable in number of 
branchings, is perceptible at a glance without the need of measurements. 
Now the arm which is thus dwarfed is always the right anterior, the one which is destined 
to disappear in the course of the modifications which produced the 3-armed form of subse- 
quent and some contemporaneous types, and the manner of the change by which that result 
was attained is apparent before our eyes. Upon first discovering this fact, I assumed that 
the change took place wholly in the Silurian ; but examination of the Ordovician species, 
especially some exceptionally well preserved specimens from the Trenton of Kirkfield in 
Ontario, showed that the tendency to atrophy of the fourth arm began much farther back. 
There are eight specimens of C. articulosus Billings or a closely allied species, in which the 
two adjacent arms are seen, and in all of them the diminution of the right anterior arm is 
almost as great as in the Tennessee species, as will be seen in figures 9 to 13 of plate 28. It is 
observable in varying degree in some of the other Ordovician species in which the arms can 
be compared, and in some the fourth arm seeius to be as large as the others. Bather (Crin. 
Goth, p. 61) observed that this arm was smallest in Castocriniis. 
Thus it is evident that we have in this instance a concrete example of the process by 
which the change from one genus to another was accomplished in the course of geological 
time. The atrophy of the two arms was clearly the direct result of pressure incident to the 
reversal and recumbent position of the crown against the stern, and v/hen the axil-arm system 
was established, the same influence was reflected in the reduced size of the branches in the 
sternward direction. 
Distribulion 
So far as known. Form A does not occur in the European areas. Its presence in the 
Silurian of Tennessee is a new and unexpected discovery. It is in the Silurian development 
of the family, as evidenced by the forms included under Form C, that the most interesting 
facts relating to distribution are found, bearing on the relation between the European and 
American faunas. About seven species of Calceocrinus have been recognized from Gotland, and 
there are at least two or three from England. Of the American species only those from the 
Rochester and Waldron formations of New York and Indiana have been heretofore figured, 
and these are mostly not in good condition for comparative study. 
The Beech River formation of Tennessee has yielded remarkable material mostlv in fine 
preservation, embracing three well-marked species suitable for comparison with European 
forms. Of these two, C. foerstei and C. bassleri, are of similar types to certain Swedish forms, 
but still are dififerentiated by good specific characters. Of the Swedish species. C. gotlandicus, 
C. pinnulatus, and C. nitidus are thoroughly distinct. Thus there are left C. pngil, C. tucanns 
and C. interpres on the other side, and C. foerstei and C. bassleri from here, through which 
a migrational connection may confidently be traced. 
No member of the family has yet been found in the European Devonian or Carbonifer- 
ous, but in America it occurs in most of the principal formations from the Ordovician to the 
middle of the Lower Carboniferous, viz.: Black River, Trenton, of the Ordovician; Roches- 
ter, Waldron, Laurel, Brownsport of the Silurian ; Helderbergian, Oriskany, Onondaga, 
Hamilton of the Devonian ; New Providence, Burlington and Keokuk of the Lower Car- 
boniferous. 
It is recognized that among the known species belonging to this family, from all three 
of the countries where it occurs, there are some which might form the types of new genera. 
One of these has been suggested by Dr. Bather, but without proposing a name. Mr. Ulrich 
has defined several others, for which he proposed names orally at the New Haven meeting 
of the Paleontological Society in 1912. It is not my purpose to enter upon these questions, 
which it is hoped will be taken up again bv those authors with a view to publication. 
