104 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



and at the base of the rays may be four times as wide as long. The 

 podial openings, one to each plate and in single ranges, are at the 

 extreme lateral edges excavated between the sutures of adjoining 

 plates and beneath the adambulacrals. Proximally, however, every 

 other podial opening progresses inwardly with the joined carinae and 

 issues where these begin to fork. Here there are, therefore, four 

 columns of podial openings in each ambulacral furrow. This change 

 is indicated by the changed position of the adambulacral plate exten- 

 sions and also b} 7 the pairs of forked carinse of the ambulacral plates. 

 Throughout the greater portion of a ray the carinse are regular and 

 alike on each plate, but toward the mouth they change rapidly in 

 direction and soon they are arranged in forked parrs, one curving 

 distally, the other proximally, with the lateral portions of each pair 

 hi contact and uniting with the extensions of the adambulacral 

 plates. The most proximal plate of each ambulacral column is 

 usually considerably modified, longer than wide, and more or less 

 triangular in outline, between which there is sometimes inserted a 

 small quadrangular ossicle. These pieces belong to the oral 

 armature. 



Interbrachial areas of medium size, with the interbrachial marginal 

 plates usually arranged in pairs but in some forms the series may be 

 terminated by single ossicles. The number of these plates in an area 

 varies in different species, there being two, three, or five inside the 

 marginal inframarginals, and all seem to be derived from the 

 inframarginal series by inward crowding. 



Genoholotype. Palseaster granulosus Meek (not Hall = P. speciosus 

 Meek). 



Distribution. Restricted to the Middle and Upper Ordovicic of 

 America, chiefly within a radius of 50 miles about Cincinnati, Ohio. 

 The following are the known species: 



P. wilsoni (Raymond). Black River (Lowville). 



P. prenuntius, new species. Trenton. 



P. sp. undet. ?Young of P. speciosus Meek. Maysvillian. 



P. speciosus (Meek). Maysvillian. 



P. granulosus (Hall). Lower Richmond. 



P. bettulus, new species. Richmond. 



P. spinulosus (Miller and Dyer). Richmond. 



P. exculptus (Miller). Richmond. 



P. wylcqffi (Miller and Gurley). Richmond. 



P. dyeri (Meek). Maysvillian. 



P. magnificus (Miller). Maysvillian and Richmond. 



Remarks. Eight of the ten species here referred to Promopalseaster 



have been described as Palxaster. They have little direct relationship 



with the latter genus in that the species are much larger, have well 



developed ambital areas, numerous accessory plates, well defined 



