MARYLAND GEOLOGICAL SURVEY 207 



ECHINODERMATA . 



CLASS CYSTOIDEA 



Family ECHINOSPHAERITIDAE 

 Genus ECHINOSPHAERI1 ES Wahlenberg 



ECHINOSPHAERITES AURANTIUM AMERICANUM n. VRP. 



Plate XLV, Figs. 15-20 



Compare Echinus aurantium Gyllenhal, 1772, Kongl. Vet. Akad. Handl., 

 vol. xxxiii, p. 245, pi. viii, figs. 4, 5; pi. 9, figs. 6-9. 



Description. One of the most interesting paleontological discoveries 

 in the Ordovician limestone of the Appalachian Valley of Pennsylvania 

 and Maryland was that of numerous large globular cystids belonging to 

 the genus Echinospherites, which had heretofore not been recognized in 

 America. One division of the Chambersburg limestone is so crowded 

 with these cystids that the name Echinospherites bed has been applied 

 to it. At first sight these cystids appear as so many boulders in the rock, 

 and indeed in the past the strata containing them have doubtless been 

 considered as conglomerates. Unweathered specimens show no definite 

 structure to these organisms other than that they appear to be globular 

 masses with a thick, smooth outer covering. When weathered, however, 

 they are seen to be composed of irregularly arranged plates with the 

 numerous canals forming the pore rhombs especially visible. 



The various species of Echinospherites seem to have been distinguished 

 by European paleontologists mainly by their differences in shape. Com- 

 paring the figures on pi. XLV with typical E. aurantium from the Middle 

 Ordovician of Esthonia, Eussia, it will be noted that the American form 

 is larger and more ovate. For this reason it has been thought best to 

 distinguish it as a variety pending a thorough study of the group by some 

 specialist. The common name of " crystal apple " applied to species of 

 Echinospherites in Europe is very appropriate, first because of their shape 

 and second because the interior of the cystid is often a mass of calcite 

 crystals. American specimens are often found with a crystalline interior. 

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