Dv. ,1 . u ,... BBYOZOA. 211 



Phylloporlna halli.] 



Obverse strongly convex, with three rather irregular rows of zooecia, their 

 apertures subcircular, with a distinct peristome, about 0.1 ram. in diameter, eight 

 or nine in 2 mm. , Acanthopores abundant, irregularly distributed, rather large, 

 especially so in the earliest forms of the species. Interspaces slightly concave, 

 occasionally faintly pitted and striated. 



In tangential sections the zooecia are rather short, with a row on each side 

 directed obliquely outward, and one series between -them. The latter are wedge- 

 shaped, and in deep sections appear as a more or less narrow central space. Dia- 

 phragms, one in each tube, have bqen observed. 



None of the other Minnesota species of the genus are closely related. All of 

 them are larger and stronger in both the branches and fenestrules. Nor are any of 

 them found in the same beds with P. reticulata. 



Formation and locality. — Both the geological and geographical distribution of this species is 

 extended. It was described originally from the Trenton limestone of New York, and in that position 

 occurs also at many localities in Canada and Vermont, and at one or two points near Cannon Falls in 

 Minnesota. In this state, however, a form occurs in the lower and middle thirds of the Trenton (Birdseye) 

 shales at Minneapolis and St. Paul, that is indistinguishable. As yet it has not been found in the upper 

 third of the shales, but, as stated, it reappears in the Galena shales (typical Trenton) near Cannon Falls. 

 It is not improbable that P. clathrata (Intrioaria elathrata Miller and Dyer), of the Cincinnati group of 

 Ohio and Kentucky, is not specifically distinct from P. reticulata. At any rate I have so- far failed to 

 detect sufficient points of difference. 



Mus. Reg. No. 5955. 



Phtlloporina. halli Ulrich. 



PLATE IV, FIGS. 16-21. 



Phylloporlna halli Ulkich, 1890. Jour. Cin. Soe. Nat. Hist., vol. xii, p. 181. 



Original description: "Zoarium an undulating foliate expansion of unknown 

 dimensions ; the largest fragment seen is 3.5 cm. iu 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 inos- 



culatiifx? 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 examples there may be a 

 secondary deposit of sclerenchyma which occasionally fills the fenestrules com- 

 pletely. 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>idth. 



