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 are 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 i^lates are elongate near the disc where 

 the arm is thicker and beconie 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 Schuchert 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 

 Astcrias has deccnded it adds one more to the list of fomis which 

 have been essentially constant for ages and after once becoming 

 fixed have varied only in very slight degrees around the type. 



Miami University. 



