CORALS AND BRYOZOA. 271 



Ptilodictya plumea, n. sp. 



PLATE LXI, FIGS. 9-12. 



ZoARiUM consisting of a flattened stipe, base conically truncated, distal extremity 

 of frond rounded. One well-preserved frond, immediately above the trun- 

 cated basal apex, is cylindrical, having a diameter of 1 mm., very gradually 

 enlarging and becoming flattened for the distance of 6 mm., where it expands 

 much more rapidly and becomes very thin ; at a point 7 mm. above the base 

 the frond is 17 mm. in width, above that point the margins are sub-parallel, 

 the frond very slightly expanding ; on other examples the margins are parallel 

 and the frond continues of uniform width"; transverse section flattened-lenticu- 

 lar, greatest thickness .30 mm.; non-celluliferous marginal space obsolete. Cells 

 tubular, oblique for the greater portion of their length, but usually opening 

 directly outward. The cylindrical basal portion of the frond is striated ; 

 striaB conspicuous, sharp, interrupted, granulose. Cell apertures circular or 

 broadly oval, immersed, diameter about .18 mm., separated by from one- 

 third to one-half the diameter of an aperture, generally irregularly disposed, 

 but sometimes forming sub-regular intersecting rows oblique to the axis 

 of the frond. Near the margins the cell apertures are oblique to the axis 

 and present a confused appearance. Peristomes obsolete. Interapertural 

 space elevated, convex or angulated, granulose, usually only one series of 

 granules between adjacent apertures, but occasionally two, sometimes, where 

 the apertures are disposed in intersecting rows there are more prominent 

 nodes at the angles of the interapertural ridges. The surface is marked by 

 low convex monticules, the centers of which are distant about 2 mm. ; the 

 apertures on these are a little larger than the others, and sometimes present 

 a slightly confused arrangement. 



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Formation and localily. Hamburg-on-the-Lake, Erie county, N. Y. 



