264 PALEONTOLOGY OF OHIO. 



apparently solid, rounded or stellate areolas, of an average diameter of 

 two-thirds of a line, which are not occupied by the cells, but which ex- 

 hibit an obscurely pitted surface. 



In its superficial characters this form might readily be taken for a 

 Fenestella, whilst the character last mentioned gives it somewhat the 

 aspect of certain species of Chastetes (Monticulipora). Its internal struc- 

 ture, however, proves it, beyond all question, to be a genuine Ptilodictya; 

 and I am not acquainted with an}- other species -of the genus with which 

 it could be confounded. 



Position and locality : Cincinnati group, Cincinnati, Ohio. The specimens examined 

 are from the cabinet of Mr. U. P. James. 



Fenestella nervata, K'icholson. 



Plate 25, figs. 11, 11a. 

 Frond fan-shaped, (?) composed of narrow, closely approximated 

 branches, about four or five of which occupy the space of one line. On 

 the non-celluliferous side of the frond are two strong, slightly diverging, 

 rounded ribs, about half a line in diameter, resembling the midribs of a 

 multicostate leaf. From the sides of these ribs the branches spring 

 obliquely, being directed in opposite directions on opposite sides of the 

 rib, with which they make a very acute angle (ten degrees or less). 

 Fenestrules long and narrow, nearly twice as long as wide, about three 

 in the space of one line measured vertically, and five in tne same space 

 measured transversely. For the most part, the fenestrules do not alter- 

 nate in contiguous rows, but are placed opposite to one another. The 

 narrow and rounded dissepiments are thus also placed nearly or quite 

 opposite to each other. Branches faintly striated in a longitudinal 

 direction. Celluliferous side unknown. 



The example of this species from which the above description is taken 

 is imperfect, and the ribs from which the branches rise are placed two 

 lines apart near the base, and four lines apart near the summit. It 

 would seem most probable that the ribs spring from a common root, and 

 that there were many of them in the perfect frond. The species is dis- 

 tinguished not only by the possession of these ribs, but also by the long, 

 narrow fenestrules, which are not placed alternately, but are so disposed 

 that the dissepiments connecting contiguous branches become opposite 

 or sub-opposite. 



Position and locality : Summit of the Niagara formation (in strata representing the 

 Guelph formation of Canada), Cedarville. Collected by Prof. Edward Orton. 



