198 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



entiated by its smaller size, less numerous plates, and by the rela- 

 tively greater size of the disk ossicles. 



SCHUCHERTIA LAXATA, new species. 

 Plate 32, fig. 3; plate 33, figs. 2, 3. 



The best specimen measures: R= 18 mm., r= 6 mm., R = 3r. The 

 University of Chicago individual: K, = 23 mm., r= about 8 mm. 

 R = 2.8r. Other specimens indicate a growth twice as large as the 

 former one. 



Kays short and slender. Disk and interbrachial arcs large but not 

 nearly so large as in Petraster speciosus. Six specimens are known, 

 four of which are poorly preserved and but a jumble of plates. The 

 specific name is given to indicate the generally separated condition 

 of the plates. 



Abactinal areas of rays and disk composed of very numerous, 

 small but irregularly sized, subquadrate or diamond-shaped, slightly 

 pustulose plates. The arrangement is mainly in quincunx but a 

 columnar arrangement is also noticeable. 



Madreporite not distinguishable amongst the abactinal plates. 



Ambulacral furrows very narrow, hardly revealing the carinated 

 ambulacral plates. The podial openings are between the plates 

 along their lateral corners. 



Adambulacral plates very convex, a little wider than long, with 

 the inner edge more or less pointed, against which terminates the 

 carina of the ambulacral pieces. There are about 15 of the former 

 plates in 15 mm. along the base of the columns. Actinally the adam- 

 bulacral columns are the most conspicuous, since the inframarginals 

 beyond the mid-length of the former columns appear not to be 

 separable from the adjoining interbrachial pieces. The inner side of 

 the adarabulacrals bears tufts of short blunt spines. 



Inframarginals recognizable as such only within the axils where 

 they adjoin the adambulacral columns. Just within each axil there 

 is a large single plate (axillary marginal) against which rest the infra- 

 marginal columns. These plates decrease rapidly in size distally and 

 are soon separated from one another so that the tenth piece from the 

 axil is indistinguishable in shape and size from the interbrachials. 



Interbracliial accessory plates very numerous, smallest in the 

 inner axillary areas and thence increasing rapidly to a size maintained 

 throughout the interbrachial areas. In form they are either diamond- 

 shaped or subquadrate, centrally tumid, and each plate seems to have 

 borne one central and two or three lateral spines. 



Formation and locality. — Five specimens are in the Harris collec- 

 tion, all from the Kichmond (Waynesville) , in the vicinity of Waynes- 

 ville, Ohio. A fine specimen showing the abactinal area (University 

 of Cliicago collection. No. 10982) was found 7 miles north of Hamilton, 



