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BULLETIN 1*7, UNITED STATES NATIONAL MUSEUM. 



are polygonal, thick-walled, and in contact, and the acanthopores are 

 not as well developed as usual. Other examples, however, possess 

 the arrangement of acanthopores and mesopores prevailing in the 

 typical form of the species. The tabulation of the common Kussian 

 form is exactly the same as shown in figure 11 1 / of the Minnesota 

 specimen, while tangential sections of both Ulrich's species and 

 varieties can be duplicated in slides prepared from the European 

 examples. The fragment of a zoarium shown in figure 111 a wUl 

 illustrate the growth of the Russian specimens equally well. The 

 characters of B. prs&nuntia are as follows : 



Zoarium of subcylindrical, frequently compressed, irregularly 

 dividing branches from 4 to 12 mm. in diameter. Surface without 



Fig. 111.— DEKATELLA PE^ENimTIA and varieties. 0, FRAGMENT OF A VARIETY, NATURAL SIZE; &, TAN- 

 gential section, x18, of the typical form; c, tangential section, xl8, of variety simplex; d 

 and e, small portions of two tangentul sections, x50; /, vertical section, x9, of specimen 

 ■with numerous mesopores; q, minute structure of walls in sections, x50. black klvee 

 (Decorah) shales, Minneapolis, Minnesota. (After Uleich.) 



monticules but minutely spinulose from the acanthopores which are 

 about half as numerous as the zooecia. Mesopores averaging one to 

 a zooecium, irregularly distributed and often segregated into clusters 

 to form the maculae. Zooecial apertures angular to rounded according 

 to the number of mesopores, eight to nine in 2 mm. 



The characters of the typical form, as seen in tangential sections, are 

 illustrated in figures 111 & and e, while the vertical section is essen- 

 tially as shown in figure 111/. 



Occurrence. — Not uncommon in theWassalem beds (D3) at Uxnorm 

 (Cat. No. 57289, U.S.N.M.), and in the Kuckers (C2) at Reval (Cat. 

 No. 57290, U.S.N.M.), Esthonia. The American specimens are 

 abundant in the various divisions of the Black River (Decorah) 

 shales of Minnesota and Iowa. 



British Museum, one specimen from the Wassalem beds at Uxnorm. 



