from the Sllnn'dii L'ncks of North America. 181 



rendering its eeneric affinities very uncertain, owing to the 

 impossibility of making out the details of its internal structure. 

 It has, however, some affinity with Ptilodictya (?) raripor<t^ 

 Hall, from the Clinton Group ; and I have therefore referred 

 it provisionally to this genus. 



Locality and Formation. — Cincinnati Group, near Cincin- 

 nati, Ohio. Collected by Mr. U. P. James. 



5. Ptilodictya fenestelliformis^ Xicli. PI. XIV. figs. 5-5 h. 



Polyzoary palmate or subpalmate towards the base, dividing 

 distally into small branches. Basal expansion and branches 

 flattened and sharp-edged, the branches being acutely elliptical 

 in cross section, and about three fourths of a line in thickness 

 centrally. Cells covering the whole surface on both sides, 

 with the exception of the sharp lateral margins, which are 

 non-celluliferous, as well as of certain non-poriferous areas to 

 be subsequently noticed. The cells on the two aspects of the 

 flattened frond respectively have their bases separated by a 

 thin laminar axis. The cells in the middle of the frond are 

 about three eighths of a line in height, gradually diminishing 

 towards the margins. Cell-mouths ovate, slightly longer than 

 broad, arranged in longitudinal rows, alternate or subalternate 

 in contiguous rows ; about five cells in one line measured 

 longitudinally, and six in the same space measured diagonally. 

 The longitudinal spaces between the rows of cells are broad 

 and slightly elevated, and are faintly striated longitudinally 

 or obscurely punctate. On the other hand, the spaces between 

 the ends of the cells are very much naiTower ; and the surface 

 thus closely resembles that of a small Fenestella-'-th.e. cell- 

 mouths looking like '4enesti-ules," the longitudinal interspac s 

 between the cells representing the "interstices," and the narrow 

 spaces between the ends of the cells corresponding with the 

 " dissepiments." The only specimens examined exhibit nu- 

 merous, apparently solid, rounded or stellate areolee, of an 

 average diameter of two thirds of a line, which are not occu- 

 pied by cells, but which exhibit an obscurely pitted smlace. 



In its superficial characters this form might readily be taken 

 for a Fenestella, whilst the character last mentioned gives it 

 somewhat the aspect of certajn species of Chcefetes [Monticii- 

 lipora). Its internal structure, however, proves it beyond all 

 question to be a genuine Ptilodictya ; and I am not acquainted 

 with any other species of this genus with which it could be 

 confounded. 



Locality and Formation. — Cincinnati Group, near Cincin- 

 nati, Ohio. Collected by Mr. U. P. James. 



Ann. cO May. N. Hist. Ser. 4. Vul. xv. 13 



