PALEONTOLOGIC CONTRIBUTIONS 59 



which lying between the ambulacralia is usually hidden from view, 

 but here exposed where the ambulacral plates are partly broken 

 away. There also the side branches are seen which lead through 

 the ambulacrals to the circular depressions, seen in the casts as 

 nodes, which served for the ampullae or for these and the podial 

 insertions (see text fig. 21 ). 



Under water the picture is entirely different. Here the casts of 

 the canals and the depressions are obliterated and the outlines of 

 the system of plates, as well as the disk, become distinctly visible 

 (see pi. XVII, fig. i). One sees there four columns of plates in 

 the ray, namely, the alternating columns of smaller subrectangular 

 plates, the ambulacrals ; and two marginal columns of slightly 

 larger, somewhat transversely oblong plates, the adambulacrals. 

 As Schondorf has shown, the ray of the Auluroids consists only of 

 four columns of plates, which form the actinal and abactinal sides. 

 It is hence the entire plate system of the brittle-star visible under 

 water. 



The oral area is clearly seen. The syngnaths appear as small, 

 hooklike slightly converging or almost parallel slits (molds) in 

 the rock. The remainder of the oral skeleton can not be made out. 



The madreporite has not been observed. The disk is distinctly 

 seen only under water. It appears. then as a dark stain. , Where best 

 preserved it possesses a concave margin and is slightly alate on the 

 rays. Marginal plates could not be distinguished, the margins being 

 all more or less torn. 



The rays are 9 + mm long, the radius of the disk is about 3 mm. 

 There are about twelve plates in each column. 



In its general outline, notably the blunt extremities of the rays, 

 the small size of the organism and the relatively small disk, this 

 species is most similar to Encr in aster (Aspidosoma) 

 s c h m i d t i Schondorf from the Lower Devonian Siegener beds 

 of Germany. 



Hallaster, Squamaster 



Plate 19; plate 20, figure 2 



The Paleozoic rocks of this State have furnished several mono- 

 typic 1 genera which, being based on a single species and sometimes 

 on a single specimen, have remained imperfectly known to this 

 day. Two closely related genera of this group are Hallaster 

 Stiirtz and Squamaster Ringueberg. The former was proposed for 

 Hall's species _Protaster forbesi from the Coeymans 

 limestone of the Helderbergian series and the other for a species 



