233 Systematic Paleontology 



Genus TETRACYSTIS Schuchert 



Tetracystis chrysalis Schuchert 



Plate XXXII, Figs. 10, 11 



Tetracystis chrysalis Schuchert, 1904, Smith. Misc. Col., vol. xlvii, pt. ii. 

 No. 1482, pp. 218, 219; pi. xxxiv, figs. 9, 10; pi. xl, figs. 1-3; text fig. 25. 



Description. — Ambulacra uarro^v, depressed, not excavated into the 

 thecal plates, and extending to the column. Ambulacrals very long and 

 narrow, about 20 in a column. Ambulacralia extremely small, about 12 

 to 14 to each ambulacral. Brachioles very slender, about 11 on each side 

 of an ambulacriTm or about 88 to each theca; length unknown. 



Pectinirhombs each with from 25 to 35 dichopores. 





Pig. 6. — Analysis of Tetracystis chrysalis Schuchert. 



Hydropore on plate 23 comparatively large and easily seen ; immediately 

 behind it is a shallow pit with numerous pores, indicating the madreporite. 



Anal area very prominent owing to the elevated anal margins of plates 

 7, 8, 13, and 14, and composed of an outer circle of 17 small pieces and a 

 highly elevated pyramid of 7 pieces. 



Column unknown. 



Length of theca of type 23 mm. ; width 17 mm. ; depth 13 mm. A 

 single specimen has a length of 24 mm. ; breadth 15 mm. ; depth 13 mm. 

 For general form, shape of individual plates and their ornamentation, see 

 the figures and diagram, fig. 6. 



Occurrence. — Helderbero Formation, Tveyser Member. Keyser, 

 West Virginia. 



Collection. — U. S. National Museum. 



