REVISION OF PALEOZOIC STELLEROIDEA. 163 



are introduced outside of the inframarginals and the entire abactinal 

 skeleton is broken up into an abunchmce of tiny pieces. Therefore, one 

 must go back for their origin at least as far as the Pala3asteridse. In 

 this case it was not primarih^ flexibility that led to this supposed 

 ordinal change, but it was due to increase of body cavity and enforced 

 enlarging of the skeleton in the interbrachial and ambital areas, 

 making the more or less pentagonal disk. It is probable that the 

 Palasteriscidse were their descendants, while the Schocnasteridas may 

 have been the final Paleozoic representatives of the same phyletic line. 

 The Palffiosolasteridas seemingly arose in the Phanerozonia family 

 Lepidasteridce by the adoption of a flexible skeleton. 



It would, therefore, seem that the Paleozoic families of supposed 

 Cryptozonia construction are to be grouped as follows: 



Superfamily Stenasteracea, new. 



Includes families Stenasteridae and Monasteridne. 

 Superfamily Urasterellacea, new. 



Includes families Urasterellidse, Calliasterellidse, and Compsasteridse. 

 Superfamily Schuchertiacea, new. 



Includes families Schuchertiidse, Palasteriscidaj, and Schoenasteridae. 

 Superfamily Palseosolasteracea, new. 



Includes family Palaeosolasteridse. 



STENASTERID^, new family. 



Rigid, small, primitive, five-rayed Cryptozonia, witli rapidly taper- 

 ing or petaloid rays. Ambulacrals few in number and opposite in 

 an^angement. Interbrachial areas consisting of the single pairs of 

 large basal adambulacral oral armature plates. 



Abactinal skeleton unknown, but in some forms seemingly integu- 

 mentary. No spines as yet known. It is probable that this family 

 will be referred to the Auluroidea. 



Contains: 



Stenaster Bilhngs. 



Tetraster Nicholson and Etheridge. 



Genus STENASTER Billings (emend.). 

 Plate 32, fig. 1. 



Stenaster Billings, Geol. Surv. Canada, Can. Org. Rem., dec. 3, 1858, p. 77. — 

 Sttjrtz, Palseontograpliica, vol. 36, 1890, p. 220. — Gregory, Geol. Mag., 

 dec. 4, vol. 6, 1899, p. 352. — Spencer, Men. Brit. Pal. Asterozoa, pt. 1 

 (Palseontogr. Soc. for 1913), 1914, p. 22. 



Urasterclla Sturtz (not McCoy), Verb, naturh. Ver. preuss. Rlieinl., etc., vol. 

 50, 1893, pp. 40, 41 , 50. 



Generic characters.— Small rigid asterids, the largest exam])le having 

 R = 20 mm., r = 4.5 mm. Disk small, witliout interbrachial arcs. 

 Rays five, short, stout, lanceolate or petaloid. 



Abactinal area devoid of a preservable skeleton. For this reason 

 when this side is at hand it is nearly always mistaken for the actinal, 

 so nearly alike are the two. 



