CORALS AND BRYOZOA. 221 



and the absence of comparatively strong conical nodes between the cell 

 apertures : from F. multaculeata by the more delicate appearance of the surface 

 of the frond, the smaller and more broadly oval cell apertures, and the absence 

 of minute spines on the peristomes and at the angles of the margins of the 

 mesopores : from F. minuta by the smaller cell apertures, the much smaller 

 mesopores, and the difference in the arrangement of the cell apertures, which, 

 in that species, are disposed so as to give a striated appearance to the surface : 

 from F. intercellata, of the Upper Helderberg group, by the finer appearance of 

 the surface of the frond, the smaller cell apertures, and the much thinner 

 walled mesopores ; in manner of growth, habit and general appearance it most 

 nearly resembles F. tegens of this geological formation, but the cell apertures 

 are slightly larger and more oval, the mesopores are larger, and generally only 

 one series between adjacent apertures, while in that species there are usually 

 two and sometimes three series : from F. densa it is distinguished by the smaller 

 and more distant cell apertures, and the absence of maculte composed of larger 

 apertures : from F. decipiens by the smaller, more regularly oval cell apertures, 

 and the much smaller mesopores. 



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

 New York. 



FiSTDLIPORA INVOLVENS, n. sp. 

 PLATE LIX. FIG. 2. 



ZoARiDM consisting of thin foliaceous expansions, incrusting other objects ; 

 greatest observed thickness less than .50 mm. Cell apertures nearly cir- 

 cular or broadly oval, diameter about .15 mm., irregularly disposed, usually 

 separated by more than the diameter of an aperture. Peristomes thin, not 

 elevated above the surrounding surface, the apertures frequently appearing 

 immersed. Mesopores very minute, from two to four ranges between adja- 

 cent apertures ; margins equal to or higher than the peristomes. 



This species most nearly resembles F. micropora, but may be distinguished 

 by the more nearly circular cell apertures, their wider separation, the more 

 minute mesopores, and the greater number of series between adjacent cell 



