Ph^enopora.] BEYOZOA. 175 



This form is easily distinguished from all the branching Clinton group species 

 of the genus by the longitudinal arrangement of the mesopores. It is, however, 

 especially in its internal structure, very similar to, and perhaps a descendant ofy 

 Escharopora (?) limitaris. Still, its branches are narrower and more rigid, and there 

 is not that difference in the size of the central and marginal rows of zocecia that 

 pertains to that Minnesota species. 



Formation and locality.— Trenton limestone, Montreal, Canada, and Chimney Point, Vermont. 

 Recently a fragment apparently identical with the eastern types of the species was collected at St. Paul, 

 Minnesota, by the author, in the Galena shales. 



Collectors, Mr. T. C. Curry and Prof. Henry M. Seely. 



Ph^nopora wilmingtonensis n. sp. • 



PLATE XIII, FIGS. 22-26; 



Zoarium a simple lanceolate frond, straight or slightly curved, tapering to a 

 point below, 40 to 100 mm. or more in length, 6 to 24 mm. wide, and 1.0 to 2.5 mm. 

 thick at the center; edges acute, non-poriferous margin inconspicuous, surfaces 

 gently convex, sometimes a little flattened on each side of the center, exhibiting, 

 according to the width of the frond, from one to ten rows of low monticules. The 

 latter occur at intervals of 2 or 3 mm., are usually arranged in rather irregular 

 longitudinal and diagonal rows, and occupied by greater or smaller aggregations of 

 mesopores and zocecia, the latter of slightly larger size than the average.- Zocecial 

 apertures subcircular or ovate, arranged in regular diagonally intersecting and 

 transverse rows ; often, especially in the lower half of the zoarium, with the enclosing 

 rim depressed at the ends, in which case they appear to be longitudinally confluent. 

 Longitudinal interspaces depressed, generally with two small mesopores, one just in 

 front of, the other immediately behind each aperture. Toward the center of the 

 monticules the number of the mesopores in each interspace is gradually increased 

 to four or more. Measuring lengthwise, about twelve apertures in a direct line 5 mm. 

 long, and twenty -three or twenty- four of the transverse rows in the same distance ; 

 diagonally, twenty, and transversely twenty-three or twenty-four in 5 mm. 



In tangential sections the base of the primitive cells is greatly elongate and 

 bounded by subparallel sides and slightly oblique end walls. Very soon after, the 

 anterior two-thirds is swollen and a curved hemiseptum thrown out from one side, 

 which continues till.it joins the opposite wall, thus enclosing the primitive aperture. 

 Preceding this the walls are very thin, but now they add to their thickness by 

 internal deposit. At the same time the aperture assumes a more rounded shape, the 

 walls approach laterally so that each cell is, normally, in contact, with six of its 

 neighbors. Between these points there is a triangular open space or mesopore. 



