EAELY PALEOZOIC BKYOZOA OF THE BALTIC PROVINCES. 329 



quently plainly evident to the unaided eye. The apertures are usu- 

 ally large, angular, thin-walled, with few mesopores, but in young 

 specimens particularly mesopores are more numerous and sometimes 

 completely isolate the zocBcia. Six zooecia in 2 mm. 



The internal characters are essentially the same as in H. multi- 

 tahulata. The vertical section figured shows the average distribution 

 of diaphragms, but in other examples the peripheral zone is broader 

 and contains more numerous diaphragms. Here also it is to be ob- 

 served that the mesopores are most common in the early part of the 

 peripheral zone and pinch out before the surface is reached. This 

 causes the variation to be observed in tangential sections. Such a 

 section passing through the early part of this outer region shows, as 

 seen in figure 205 l, rounded zooecia more or less separated by meso- 

 pores. The zooecia in a section taken just below the surface are 

 angular, partly in contact, and mesopores are comparatively few. 



Comparing H. wesenbergiana with H. multitabulata, its closest ally, 

 it is found that the latter has smaller zooecia (eight in 2 mm.), a 

 tuberculated surface, and a more regular zoarium. The associated 

 H. goodhuensis is also quite similar, but differs in having a small, 

 more regularly branching zoarium, with smaller zooecia and more 

 regularly dividing branches. Indeed, these three species have so 

 much in common that it requires close discrimination to separate 

 them. 



Occurrence. — Extremely abundant in the Wesenberg limestone (E) 

 at Wesenberg and other localities in Esthonia; less common in the 

 Wassalem beds (D3) at Uxnorm. The same species, or at least a 

 closely related variety, occurs rarely in the Orthoceras limestone (B3) 

 at Reval. 



Plesiotype.—C&t No. 57462, U.S.N.M. 



Specimens and thin sections from the Wesenberg limestone at 

 Wesenberg, are in the collections of the British Museum. 



HALLOPORA SPLENDENS, new species. 



Text fig. 206. 



Cfr. Callopora ampla Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 

 1893, p. 281, pi. 23, figs. 13-15, 18-20, 22, 23, 27, 28. 



Zoarium of irregularly divided, stout, subcylindrical branches 

 averaging 10 mm. in diameter. Surface smooth, maculae inconspicu- 

 ous, 3 mm. distant from each other and made up of zooecia slightly 

 larger than the average. Zooecia direct, angular, with rather thick 

 walls for the genus, 5 in 2 mm. Zooecial aperture often preserving 

 ornamented opercula. Mesopores almost entirely absent at the sur- 

 face but visible in vertical sections in the bend from the immature 

 to the mature region. Ornamented opercula or closures are pre- 

 served on a few of the specimens. 



