EAKLY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 327 



zooecia are often closed with ornamental opercula, as shown in figure 

 202 c. Mesopores are few. The most marked internal feature is 

 the crowded tabulation shown in figure 202 d. In the immature zone 

 the diaphragms are seldom more than their own diameter apart and 

 frequently more closely spaced. In the mature zone six or seven 

 diaphragms may frequently be counted in the space of a tube diam- 

 eter. The few mesopores present are equally crowded. 



Occurrence. — ^Abundant in the Black River and Lower Trenton 

 strata of Minnesota, Iowa, Kentucky, and Tennessee. Less common 

 in the Wassalem beds (D3) at Uxnorm, Esthonia (Cat. No. 57459, 

 U.S.N.M.). 



Represented in the British Museum by a specimen and thia section 

 from Uxnorm. 



HALLOPORA GOODHUENSIS (Ulrich). 



Text figa. 203, 204. 



Callopora goodhuensis Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 

 1, 1893, p. 282, pi. 23, figs. 9, 10, 21, 29. 



This bryozoan is closely related to Hallopora multitabulata (Ulrich), 

 but differs in that the surface is without monticules, the average size 

 of the branches is less, the zooecia are smaller, especially at the center 

 of transverse sections, and their apertures are subangular and slightly 

 smaller. The internal structure is very similar, the most marked 



Fig. 203.— Hallopoea goodhuensis. a and 6, two fkagments of natukal size; c, sueface of a speci- 

 men, X9; d. AXIAL eegion of a teansveese section, X18. Clitambonites bed of the lower Teen- 

 ton limestone, neae Cannon Falls, Minnesota. (Aftee Uleich.) 



difference being that the mature region is narrower. The internal 

 structure of a well developed Russian example is shown in figure 204. 



Occurrence. — ^Abundant in the Clitambonites bed of the Lower 

 Trenton at St. Paul and other localities in Minnesota; not uncommon 

 in the Wassalem beds (D3) at Uxnorm, and in the Wesenberg lime- 

 stone (E) at Wesenberg, Esthonia. 



Plesioty pes. —C&t. Nos. 57460, 57461, U.S.N.M. 



British Museum, specimens and thin sections from Uxnorm. 



