114 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



A more important distinguishing character exists in the inter- 

 brachial areas. In P. heUulus and P. speciosus there are two pairs 

 or four interbrachial marginal plates, while the number of adjoining 

 adambulacral plates is greater. In the latter there are four of these 

 on each side, while in the former there are eight. In other words, 

 the interbrachial areas in P. heUulus are much more elongated orally 

 than in P. speciosus and the interbrachial arcs are also greater. 



Abactinally on the rays the arrangement and number of columns 

 of plates appear to be very much like those in P. speciosus. The 

 individual plates are, however, less convex, cruciform, more like thos.e 

 of P. spinulosus, and have stronger and more abundant spines. The 

 spines in P. hellulus are very numerous, short, and slender, and are 

 inserted one on the apex of each plate and a number around the sides 

 in the angles between the radial extensions. In P. speciosus the spines 

 are grouped over the convex area of the plate and around the larger 

 central spine. The arrangement of the plates of the disk appears to 

 have no marked pattern and consists of very numerous small plates 

 like those of the rays. 



The adambulacral plates each bear three spines as in P. speciosus 

 and increase in size toward the base of the rays. One is inserted on 

 the inner or ambulacral face of the plate and the two closely adjoining 

 ones immediately above and laterally on the rounded surface. 



Ambulacral plates as in P. speciosus. 



Madreporite of medium size, subcircular in outline, with numerous 

 straight, sharp, radiating ridges. It is inserted proximally between 

 two adjoining columns of supramarginal plates. 



A development occun-ing only in this species of Promopalseaster 

 is a single plate oral to the proximal adambulacrals. This plate 

 has been seen in four axillary areas. It may be a modified ambu- 

 lacral and may correspond to a similar plate, which is an ambulacral, 

 in P. exculptus. 



Formation and locality. — Of this species quite a number of speci- 

 mens were secured by Mr. Harris in the WaynesviUe beds of the 

 Richmondian. They are aU in the United States National ]\Iuseum. 

 One excellent specimen (the holotype) showing the actinal area, 

 and two smaller poorer specimens are attached to limestone, while 

 eleven fair specimens and fragments of eight other individuals are 

 from a soft blue shale associated wdth Zygospira modesta and Ptilo- 

 dictya shafferi (upper form). All were secured in the vicinity of 

 Waynesville, Ohio. The shale specimens were exhumed from one 

 small area, showing that probably many starfishes could be similarly 

 secured by collectors, since these soft specimens in weathering out 

 are broken up and lost; more asterids will be found when they are 

 dug or quarried for. Another good specimen is in the Gurley col- 

 lection of the University of Chicago (No. 10983) and was found at 

 Versailles, Indiana. 



