220 PALEONTOLOGY OF NEW YORK. 



mesopores ; in that species the cell apertures are sometimes polygonal, and it 

 is frequently difficult to distinguish the apertures from the mesopores : from 

 F. conferlipora by the smaller and more distant cell apertures : from F. tegens 

 by the larger cell apertures and mesopores : from F. minuta by the more distant 

 cell apertures and their more irregular disposition : on that species they are 

 generally so arranged that the peristomes and margins of the mesopores give a 

 striated appearance to the surface of the frond : from F. digitata by the larger and 

 more distant cell apertures, the larger mesopores, and the absence of compara- 

 tively strong nodes between the cell apertures : from F. densa by the larger 

 and more distant cell apertures, and the absence of maculae composed of 

 larger cell apertures : from F. intercellala, of the Upper Helderberg group, by its 

 more nearly circular and more distant cell apertures, thinner peristomes and 

 larger mesopores. 



Formation and locality. Hamilton group, Eighteen-Mile creek, Erie county. 

 New York. 



FiSTULIPOKA MICROPOKA. 



PLATE LVII, FIG. 20 ; AMD PLATE LIX, FIG. 3. 



Thallogligma micropora, Hall. Trans. Albany Institue, vol. x, p. 186. 1881. 



Report of State Geolo^st for 1883, p. 26. 1884. 



ZoARiDM consisting of very thin lamellate expansions, incrusting other objects, 

 especially crinoid columns ; greatest thickness observed .33 mm. Inter- 

 cellular tissue vesiculose. Cell apertures broadly oval, frequently nearly 

 circular, length about .18 mm. or less ; irregularly disposed, varying from 

 contact to a space equal to the width of an aperture. Peristomes thin, 

 equally elevated, and smooth on the specimens observed. Mesopores minute, 

 about ten in the space of 1 mm., generally only one series between adjacent 

 apertures, rarely two ; margins of the same height as the peristomes. 



This species may be distinguished from F. segregata by the thinner fronds, 

 the smaller cell apertures, their closer arrangement, and the more delicate 

 appearance of the surface of the frond : from F. digitata by the diffijrent 

 manner of growth, the smaller cell apertures, their less frequent occurrence. 



