1888 .] 
117 
[Hitchcock. 
2. Hook-shaped spines found one on each side of the terminals 
of the very young Ophiothrix, Ophiocoma and others, and on sev- 
eral plates in Astrophyton, Ophiobrachion and others in the adults. 
Both kinds of spines are movable. 
In addition we have also : — 
3. Fins of Ophiopteron. 
4. Fan-shaped spines of Asterias. 
The function of the hooked spines in Astrophyton is not doubt- 
ful to any one who studies the living animal. They are in this genus 
grasping organs. It is more difficult to say what function they per- 
formed in the larval Ophiothrix. Their absence in the viviparous 
Amphiura may possibly throw some light on this question. 
A more pertinent question in our discussion is whether these 
hooked spines on the young Ophiocoma and Ophiothrix are homol- 
ogous with the fan-shaped spines of Asterias and the spatulate 
spines of Arbacia. This question is a difficult one for us to an- 
swer from the fact that so little is known of their manner of de- 
velopment and their primary relation to the terminals and other 
plates. We are certainly justified in supposing that they are ho- 
mologous, as far as all movable spines may be homologous, but we 
must wait until we have more observations to prove that these 
hook-shaped spines are homologues of the fan-shaped spines of 
Asterias or the spatulate spines of Arbacia. 
General Meeting, December 19, 1888. 
The President, Prof. F. W. Putnam, in the chair. 
The following papers were read : 
RECENT PROGRESS IN ICHNOLOGY. 
BY C. H. HITCHCOCK. 
The study of Ichnology in our country commenced in Massa- 
chusetts, whose legislature published the Ichnology in 1858 and its 
Supplement in 1865. Since the appearance of these reports exca- 
vations have been made at Turner’s Falls by Roswell Field, Prof. 
O. C. Marsh, T. M. Stoughton and others, and very valuable slabs 
obtained. Other localities have been explored to a less extent. 
The study of the Ichnozoa, or the animals that made the tracks, 
naturally divides itself into three parts : first, an examination of 
