BRYOZOA. 275 



Calloporidfe.l 



with a gentle curve, the walls become thickened and the diaphragms more abund- 

 ant, the'intervals between the latter varying here from one-fourth to one tube- 

 diameter, with seven in 1 mm. measuring from the surface of a fully developed 

 example. Acanthopores originating in the outer part of the axial region, large and 

 readily distinguished. Tangential sections with the walls rather thick and consist- 

 ing of a central space, generally of light color, representing the original walls, and 

 a dark ring-like deposit immediately about the zooecial cavities. On the whole the 

 structure and thickness of the walls is much as in Dekayella prainuntia, var. simplex 

 (pi. XXIII, figs. 41 and 42). The acanthopores are isolated, occupying the points of 

 junction between every three, four or five zocecia. Their large size makes them very 

 conspicuous in sections passing through deeper levels in which the walls are thinner 

 than described. 



In this species the diagnostic characters of Dekayia are not yet fully developed, 

 the diaphragms being too numerous. . A revision of the Heterotrypidce would prob- 

 ably remove it to Dekayella. A more typical, but undescribed species, with fewer 

 diaphragms and smaller acanthopores, is sometimes associated with D. trentonensis 

 in the Galena shales. Dekayella echinata, which at first I confounded with the 

 present species, has more numerous diaphragms, thinner walls, and a small set of 

 acanthopores. 



Formation and locality. Rather rare in the upper third of the Trenton shales and in the overlying 

 Galena shales at St. Paul, and near Cannon Falls, Minnesota. The original types are from the shaly por- 

 tion of the Trenton at Burgin, Kentucky. The species is to be found also at Frankfort and other localities 

 in that state, associated with Prasopora simulatrix Ulrica. 



Family CALLOPORID^, Ulrich. 

 Genus CALLOPORA. Hall. 



Callopora, HALL, 1852, Pal. N. Y., vol. ii, p. 144, and 1887, Pal. N. Y., vol. vi, p. xv; NICHOLSON, 1874, 



Pal. Ontario, p. 61, and Geol. Mag., n. s., vol. i, p. 13; ULRICH, 1882, 

 Jour. Cin. Soc. Nat. Hist., vol. v, pp. 154 and 251; also 1890, Geol. Sur. 

 111., vol. viii, pp. 372 and 410; FOERSTE, 1887, Bull. Sci. Lab. Denn. 

 Univ., vol. ii, p. 172. 



f Callopora, DYBOWSKI, 1877. Die Chsetetiden, p. 106. 



Zoarium usually ramose, rarely subfrondescent, or pyriform; surface smooth or 

 tuberculated. Zocecial tubes with thin walls, varying according to the number of 

 mesopores from circular or oval to polygonal in cross-section. Apertures closed in 

 the perfect state by centrally perforated and often radially marked or oi'namented 

 plates, which are left behind as growth proceeds to form floors (diaphragms) of 

 succeeding layers. Mesopores angular or rounded, more or less numerous, some- 

 times surrounding the zooecia; closely tabulate. Zooacial tubes attaining their full 



