118 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



strong spines, and some of them, preserved on our specimen, have 

 a length greater than the length of a plate, * * * 



"The ambulacral plates have their greatest length across the rays, 

 thus providing a wide ambulacral furrow. Each plate is furnished 

 with a sharp ridge in the middle, that curves slightly outward, from 

 the center toward the adambulacral range, increasing in height 

 until it approaches or abuts against the adambulacral plate. * * * 

 The appearance of having been carved out, which is presented by 

 the ambulacral plates, suggested the specific name. [The plates of 

 adjoining columns are opposite one another or slightly alternate.] 



"The dorsal side and madreporiform tubercle unknown." 



Supplementary description. — R = 37 mm., r=l2 mm., R = 3.1r'. 

 The specimen is very much flattened and the exact width of a ray 

 can not be given but appears to have been about 10 mm. at the base. 



In the axils of the rays the proximal inframarginal plates of adjoin- 

 ing rays rest against each other, inside of which are two wedge-shaped 

 interbrachial marginal plates. Orad to these and adjoining the pairs 

 of proximal adambulacrals (oral armature pieces) is situated a single 

 subquadrate ossicle, making three interbrachial marginal plates in 

 each interbrachial area. 



The podial openings in the ambulacral grooves are between the 

 sutures of adjoining adambulacral and ambulacral plates along the 

 line where these two columns adjoin. The proximal ambulacral 

 plates orad to the axial adambulacrals are considerably modified 

 and are to be considered as parts of the oral armature. A single 

 rather large plate is here partially wedged between the pair of termi- 

 nating adambulacrals, and on each end of it abuts a single broadly 

 triangular plate, a modified ambulacral, completing the oral ends of 

 the ambulacral columns (see drawing, pi. 20, fig. 2). 



Formation and locality. — In the Richmond formation near Waynes- 

 ville, Ohio. The holotype and only specimen is in the Harris collec- 

 tion of the United States National Museum. 



RemarTcs. — This species is near P. spinulosus, but apparently had 

 wider, shorter, and more rapidl}^ tapering rays. There appear to be 

 but two interbrachial marginal plates in P. spinulosus, while P. 

 exculptus has three in each area. Should the former species also prove 

 to have three plates, a possibility, P. exculptus will be actinally 

 identical with P. spinulosus. The wider and more rapidly tapering 

 rays of P. exculptus can then be explained by the fact that the type- 

 specimen is considerably distorted, since the adambulacrals and infra- 

 marginals now lie wholly outside of the ambulacrals, which are com- 

 pletely exposed, an unnatural condition. So long as the abacti- 

 nal area of P. exculptus remains unknown the species had best be 

 retained. 



Cat. No. 60608, U.S.N.M. 



