PALEONTOLOGIC CONTRIBUTIONS 



119 



are transversely subquadrangular in outline with proximal wings 

 curving around the podial openings proximally, as in Hallaster 

 and Taeniaster. The adambulacrals are, considering the size of 

 the ray, astonishingly strong and large plates; of halfcup shape, 

 imbricating with their distal extremities and extending far up to 

 the abactinal side where they come nearly into contact showing 

 between them the abactinal sides of the ambulacral ossicles which 

 there appear like vertebrae or thick rings with a faint median 

 suture. Along their distal edge they show evidence of fine fragile 

 spines. A column of four of these vertebralike ambulacral s can 



3» 39 



Fig- 38) 39 A r g e n t i n a s t e r b o d e 11 b e n d e r i nov. 38 Ambulacral 

 ossicles, seen from actinal side, the outline of adambulacrals in dotted line. 

 x 5- 39 Abactinal side of one ray, showing the oral frame, the middle column 

 of ambulacrals and the large adambulacrals. x 2^2 



be traced within the disk to the mouth frame. The latter is very 

 heavy, apparently simple' and bears the equally blunt, thick syng- 

 naths or mouth angle plates. The surface of the disk integument 

 and of the marginal disk plates was granular, the ray plates were 

 smooth. 



Madreporite not seen. 



Measurements. Radius of rays 20+mm ; radius of disk 5 mm. 



Horizon and locality. Silurian of Quebrada del Aguadido 

 (Yachal, Cerro Blanco), Argentine Republic. 



The general outline and the presence of the marginal disk plates 

 would suggest a small Encrinaster, but the structure of the rays 

 with their opposite ambulacrals that possess proximal wings sur- 

 rounding the podial pores ; and especially the form of the adam- 

 bulacrals, are characters connecting it with the genera Hallaster, 



