Corals and Bryozoans of the Lower Helderberg. 149 



from the surface, when they abruptly turn outward, and at this point are gen- 

 erally constricted, and the cell- walls, previously very thin, become much thicker ; 

 transverse partitions rare or entirely wanting until after the abrupt turn of the 

 tubes, when they are numerous ; length of longest cell-tubes six mm. ; diameter 

 at aperture .25 mm. ; cells of nearly uniform size, frequently spinulose at the 

 angles. 



This species may be easily recognized, when a longitudinal section can be 

 seen, by the abrupt turn of the cell-tubes to the surface, in which respect it 

 differs from any other known species of this formation. 



Formation and locality. Lower Helderberg group, Schoharie, N. Y. 



Ch^tetes tabulatus. 



(PLATE IX, FIGS. 12-15.) 



Chcetetes tabulatus, Hall. Illustrations of Devonian Fossils : Corals, plate 37, 



tig-s. 16, 19. 1876. 



Corallum forming spheroidal or hemispheric masses ; diameter of the largest 

 specimen seen a little more than four mm. ; tubes arising from the centre of the 

 base, and increasing by interstitial additions ; diameter at the apertnre about 

 .50 mm. ; cell-walls thin, transverse ; diaphragms, so far as observed, wanting ; 

 the cell-walls are strongly and quite regularly corrugated ; the corrugations are 

 nodose at the angles of the cell- walls ; about fifteen in the space of five mm. 



Formation and locality. Lower Helderberg group, Schoharie, N. Y. 

 Ch^tetes corticosa. 



(PL\TE X, FIGS. 1-10, AND PLATE XIII, FIG. 4.) 



Trematopora corticosa. Hall. Twenty-sixth Report IS. Y. State Mus. Nat. Hist., 



p. 105. 1874. 



Bryozoum ramose, solid ; branches frequent, diverging at an angle of about 

 ninety degrees ; diameter of larger branches five mm. ; cells contiguous, gener- 

 ally pentagonal, hexagonal or apparently oval from thickening of the margins, 

 arising from the centre of the branch and gradually curving to the surface, in- 

 creasing by interstitial additions ; septa strong, distant from each other by a 

 space equal to two or three times the diameter of a cell-tube ; cell-walls thickened 

 toward the apertures, frequently forming irregular ridges like the miniature 

 roughened bark of a tree. 



This species is easily recognized by its peculiarly roughened 'surface, and 

 widely diverging branches. 



Formation and locality. In the shaly limestones of the Lower^Helderberg 

 group, near Clarksville, N. Y. 



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