1 82 Cincinnati Society of Natural History. 



Zoarium an undulating foliate expansion, of unknown dimen- 

 sions; the largest fragment seen is 3.5 cm. in diameter; thickness 

 of strongest varying between 1.5 and 2.0 mm. Branches scarcely 

 distinguishable as such, the zoarium having the appearance of a 

 perforated plate rather than consisting of inosculating branches. 



Reverse with the fenestrules small, subcircular or oval, arranged 

 more or less regularly in longitudinal and diagonal series, with 

 from eight to ten in 1 cm. either way. When the arrangement is 

 regular they are approximately of the same size, but when that is 

 not the case some may be much smaller than the average. The 

 latter are about 0.4 mm. in diameter. Over portions of old exam- 

 ples there may be a secondary deposit of sclerenchyma which 

 occasionally fills the fenestrules completely. Such deposits are, 

 however, much less frequent than upon the celluliferous face. 

 Branches convex, smooth, with an average width of 0.65 mm. 

 Occasionally one may be swollen to twice that width. 



Obverse generally presenting a very irregular appearance. This 

 is largely due to irregular, noncelluliferous deposits of sclerenchyma 

 that occur at variable intervals. The fenestrules, however, also 

 seem less regularly arranged than upon the reverse face. Surface 

 of branches strongly convex, carrying from three to six or more 

 rows of alternating and scarcely circular zocecial apertures. These 

 are about 0.9 mm. in diameter, without peristomes, and separated 

 by intervals of less width generally than their diameter. Some of 

 the interspaces are a little prominent. These may have contained 

 acanthopores. Five or six cell apertures in one mm. 



Although the preservation of the material is not the best for 

 microscopical determination of internal characters, thin sections 

 still bring to light the more salient features. They show that the 

 zocecial tubes are intersected by numerous diaphragms; that near 

 their apertures they are still prismatic, resembling the zocecia of a 

 Monticuliporoid, and that a few small cells, perhaps acanthopores, 

 are scattered among the true zooecia. 



This is an easily recognized species, being also quite distant 

 from all the others of the genus known. In its proportions it is 

 somewhat like P. corticosa, from the same horizon, but they are 

 not likely to be confounded, the strong carinae on both sides of 

 the branches in that species serving amply in distinguishing them. 



The specific name is given in honor of Prof. C. W. Hall, of 

 the State University of Minnesota, who is taking a lively interest 



