220 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



T^NIASTER CYLINDRICUS (Billings). 



Plate 36, figs. 2, 3; text fig. 18. 



Palseocoma cylindrica BILLINGS, Geol. Surv. Canada, Rep. Progress for 1853- 

 1856, 1857, p. 292. 



Txniaster cylindricus BILLINGS, Geol. Surv. Canada, Can. Org. Rem., dec. 3, 

 1858, p. 81, pi. 10, figs. 4a-4c. WRIGHT. Mon. British Foss. Echinod., Oolitic, 

 vol. 2, pt. 1 (Palseontogr. Soc. for 1861), 1862, p. 34. PARKS, Trans. Cana- 

 dian Inst., vol. 8, 1908, p. 371. 



Txniura cylindrica GREGORY, Proc. Zool. Soc. London for 1896, 1897, p. 1035. 



Lapworthura cylindrica PARKS, Trans. Canadian Inst., vol. 8, 1908, p. 371. 



Original description. "One inch and a half in diameter; rays 

 five [very flexible], covered with spines, subcylindrical, regularly 



rounded on the upper side, flattened 

 on the lower, about one line in width 

 at base, and regularly tapering to an 

 acute point." 



Formation and locality. In the Tren- 

 ton limestone at Ottawa, Canada. The 



. i8.-DiAGRAMOp7cTmAL BAY-PLATES cotypes (14050), along with a third 

 OF TJSKIASTKR CYLINDKICUS BILLINGS, specimen (1405), are in the Victoria 



a, AMBTJLACKAL; ad, SIDE PLATES. _* . , v , 



Memorial Museum at Ottawa. 



T^ENIASTER SCHOHARL Ruedemann. 



Tseniaster schoharise RUEDEMANN, Bull. N. Y. State Mus., No. 162, 1912, p. 88, 

 pl. 3, fig. 1. 



Original description. The holotype "is small, the arms about 15 

 mm. long, and it is without a disk. The arms are slender and flexible, 

 about 1.3 mm. wide at the base, and almost as high in lateral view, 

 originally probably cylindrical. The ventral view shows a straight or 

 slightly zigzagged ambulacral canal, and on both sides of this squarish 

 depressions surrounded by the ambulacral and adambulacral ossicles, 

 the covering lower arm plates not being retained if they existed. 

 The inner (ambulacral or vertebral) ossicles appear as narrow and 

 outwardly curved ridges, the outer or adambulacral ossicles as ridges 

 bent in the opposite direction with a projection in the middle of the 

 outer arch. The ambulacral ossicles are not directly opposite nor 

 regularly alternating, but those of the right side on the ventral view 

 advanced about one-third the length of the ossicles beyond those of 

 the other side. 



"The lateral view of one other arm exhibits the ossicles as ver- 

 tical bars, that are thickened at both ends resembling vertebrae 

 and terminating at the dorsal side with a flat surface and forming 

 there an apparently continuous layer. They appear almost twice 

 as wide as the intervening spaces. The dorsal surface bears bundles of 

 obliquely forward directed spines, one bundle corresponding to each 

 ossicle. These spines appear in the right arm to proceed from 



