EAELY PALEOZOIC BKYOZOA OF THE BALTIC PROVINCES, 193 



ules, as shown in figure 103 c, are more common. In this figure about 

 half of the zooecia show cystiphragms cut by the section. 



The smooth branches inosculating so as to form a cribrose zoarium, 

 and the internal features shown in the figure, are sufficient to separate 

 this from similar small-stemmed species. The same species, differ- 

 ing only in having less numerous diaphragms in the immature zone, 

 occurs in the Black Kiver shales of Minnesota. 



Occurrence. — Common in the Wassalem beds (D3) at Uxnorm, 

 Esthonia; the same species, or at least a variety, is equally abundant 



d 



Fig. 103.— Homotetpella cribrosa. a, vertical section, X20, illustrating the short mature zone 

 AND tabulation; 6, tangentU-L section, X20, showing characters of the early part of the 

 mature zone in the upper half and the later part in the lower half; c, several zocecla of 

 the same section, X35. Wassalem beds (D3), Uxnorm, Esthonla. 



in the Black River (Decorah) shales at Fountain and other locaHties 

 in Minnesota. 



Holotype.— Cat. No. 57278, U.S.N.M. 



Specimens and thin sections from the Wassalem beds, Uxnorm, 

 are in the collections of the British Museum. 



HOMOTRYPELLA HOSPITALIS CRASSA (Ulrich). 

 Text figs. 104, 105. 



Atadoporella crassa Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 



1893, p. 225, pi. 15, figs. 18-21. 

 Cfr. Monticulipora (Prasopora) selwynii var. hospitalis Nicholson, Genus Monti- 



culipora, 1881, p. 209, fig. 45. 



One of the most abundant and characteristic fossils of the Rich- 

 mond formation in North America is the bryozoan described by 

 Nicholson as Monticulipora {Prasopora) selwynii var. Tiospitalis, 

 later referred by Ulrich as a valid species of Prasopora. The small, 

 more or less rounded zoarium, with zocecia having numerous acan- 

 thopores, lined with cystiphragms and separated by closely tabu- 

 lated mesopores, make this form especially easy of recognition. 

 Detailed collecting in the American Black River and Trenton hori- 

 zons resulted in the discovery of a species or variety closely related 

 to the Richmond form, and now the study of the Russian Ordovician 



