224 
The Ohio Naturalist. 
[Vol. XIV, No. 3 , 
motion as more tube feet can be crowded into a given length of 
arm. We can assume that the alternation served the same pur¬ 
pose in the fossil form. 
The adambulacral plates are 3 m. m. long by one m. m. thick. 
Their third dimension, in the vertical plane is about 2 m. m. The 
aboral ends of these plates fit in between the outer ends of the 
ambulacral plates. For this reason they are also called the inter- 
ambulacral plates. 
There is evidence that they bore a double row of movable 
spines on their oral or ventral aspect, but I am not sure that any 
of these are preserved. There are a few spindle-shaped spines 
3 m. m. long, larger near the outer end and tapering gradually to 
the point of attachment. Spines like these though larger arc the 
ones which Professor Meek calls the movable spines in P. dyeri. 
Other fragments of starfishes of undetermined species lead me 
to think that these might have been the spines broken from the 
infero-marginal row of plates and that the regular movable spine 
was more slender. 
The infero-marginal plates are elongate near the disc where 
the arm is thicker and become more nearly cubical, corresponding 
to the shape figured for P. dyeri, out near the tip of the arm. 
Some of these plates show impressions which with some 
uncertainty I consider to be the remains of pedicellaria around 
their outer surface. There are also here and there in the spaces 
between plates isolated structures which might be the larger 
pedicellaria with the basal plate and two jaws which are found 
singly in such spaces in recent starfishes. 
This specimen shows so many similarities to Palaeaster dyeri, 
the canals of the madreporite, the shapes of the spines, and of the 
infero-marginal plates that in spite of differences and pending 
the publication of an authoritative monograph on the Palaeozoic 
starfishes by Professor Sebuchert of Yale University I refer it to 
this species. 
In a letter Professor Schuchert says that the specimen certainly 
belongs to his genus Promo-palaeaster and that it may be P. 
wykoffi, P. dyeri or a new species. • 
In all events and whatever its name, we have in this fragment 
of a starfish from the Richmond division of the Ordovician sea, 
millions of years ago, the plates, the pores, the spines and probably 
the pedicellaria very similar to those which are found in the star¬ 
fishes of the present day. 
If it is in the direct line of ancestors from which our present day 
Asterias has decended it adds one more to the list of forms which 
have been essentially constant for ages and after once becoming 
fixed have varied only in very slight degrees around the type. 
Miami University. 
