REVISION OF PALEOZOIC STELLEROIDEA. 197 



angles ill contact with the oral plates are much larger than any of 

 the others. 



''In the only specimen in the collection the length of the rays 

 measured along the ambulacral grooves is three hues; number of 

 adambulacral plates on each side of the grooves sixteen; the rays 

 diminish somewhat rapidly in size, and terminate in a rounded point; 

 diameter of the disk four lines. The plates are all a little worn, so 

 that the character of their surfaces can not be observed; they were 

 probably nearl}" smooth." 



Emended description. — ^IVIeasurement of the immature type-speci- 

 men: R = 6 mm., r = 3 mm. Larger specimen: R = 9 mm., 7^=4 mm. 



Abactinal area composed of a series of plates which are more or 

 less closely adjoining and on the rays are arranged in distinct but 

 twisted columns. This twisting is due to the insertion of new columns 

 of plates, always on the right siile, crowding the older ones to the left. 

 The plates on the rays are subquadrangular to elongate subquad- 

 rangular, increasing in size proximally, and on tlie disk are largest 

 and generally subcircular in outline, or faintly stellate. The plates 

 appear to be smooth. At the apex of the ray are two somewhat 

 larger plates followed by tliree columns and on each side of these 

 there are two other columns of ossicles. Near the beginning of the 

 interbrachial arcs the rays liave from seven to eight columns of plates. 



Madreporite not distinguished among the abactinal plates. 



Actinally the most conspicuous columns are the adambulacrals 

 bounding tlie very narrow ambulacral grooves. These ossicles are 

 subquadrangular in outline near the base of the column, but become 

 wider tlian long distally; there are about 15 in a column, terminating 

 proximally in two larger, prominent, wedge-shaped plates of the 

 oral armature. Interradially upon each pair of oral pieces is placed 

 a large, single, pentagonal plate (holds the position of axillary 

 interbrachials) , against which rest two diverging inframarginal 

 columns, each with 13 or 14 ossicles, and these columns continue 

 adjoining the adambulacrals. Before attaining the distal ends of the 

 rays they gradually bccimie smaller and pass over to the abactinal 

 side. Other actinal disk plates are also present, but apparently are 

 arranged in quincunx, and are smooth like those of the abactinal side. 



Ambulacrals unknown. 



Formation and locality. — Ordovicic. The holotype (No. 1399, Geol. 

 Surv. Canada collection) showing the a(;tinal area was found by Mr. 

 E. Billings, at Ottawa. Another specimen, also in the ^luseum of 

 the Geological Survey of Canada, and showing the abactinal area, was 

 found by Mr. J. S. Stewart on Governor General Bay, near New 

 Edinburgh, Canada. 



Bemarlts. — Tliis little Ordovicic asterid is distinguishable from 

 other species with large interbrachial arcs in that it is devoid of all 

 marginal and radial columns of plates. From S. laxata it is differ- 



