270 PALEONTOLOGY OF NEW YORK. 



The surface characters are somewhat similar to those of Stidopora rhomboidea 

 of the Upper Helderberg group, but the manner of growth will readily serve 

 to distinguish it. From all other species, at present known, it may be distin- 

 guished by the clavate form of the frond. 



Formation and locality. Hamilton group, Kashong creek, Bellona, Yates county, 

 N. Y. 



PTILODICTYA, Lonsdale. 1839. 



(See page 38.) 



Ptilodictya parallela, n. sp. 



PLATK LXI, FIGS. 7, 8. 



ZoARiUM consisting of a simple stipe, having an acute base, transverse section 

 near the base circular, striated, rapidly enlarging and becoming flattened 

 above ; stipe about 3 mm. in width, the margins for the greater portion of the 

 length essentially parallel ; transverse section lenticuLar, greatest thickness 

 about .50 mm. Cells tubular, arising obliquely from the mesotheca, curving 

 and opening directly outward ; the marginal cells are slightly oblique to the 

 axis of the frond, the others are parallel. The intercellular tissue has not 

 been observed. Cell apertures circular, diameter about .20 mm., disposed 

 in longitudinal parallel rows, from ten to twelve on a branch, the apertures 

 of the rows are separated by a little less than their diameter; in the 

 central rows there are sixteen apertures in the space of 5 mm. ; in the 

 marginal rows twelve in the same space. Peristomes thin, slightly elevated, 

 the posterior portion the most prominent, and with two minute denticula- 

 tions. Ranges of apertures separated by smooth prominent ridges, about 

 one-third the width of the cell apertures ; the ridge along the middle of the 

 branch is stronger than the others and sometimes has the appearance of a 

 carina. 



Formation and localities. Hamilton group, Darien Centre, Genesee county, and 

 near the hea<l of Canandaigua lake, Ontario county, N. Y. 



