LIST OF ILLUSTRATIONS. 



PLATES. 



Facing page. 



1. Geologic map of the Russian Baltic Provinces. (After von Schmidt.) 350 



2. Early Paleozoic Bryozoa of the Baltic Provinces 352 



3. Early Paleozoic Bryozoa of the Baltic Provinces 354 



4. Early Paleozoic Bryozoa of the Baltic Provinces 356 



5. Early Paleozoic Bryozoa of the Baltic Provinces 358 



6. Early Paleozoic Bryozoa of the Baltic Provinces 360 



7. Early Paleozoic Bryozoa of the Baltic Provinces 362 



8. Early Paleozoic Bryozoa of the Baltic Provinces 364 



9. Early Paleozoic Bryozoa of the Baltic Provinces 366 



10. Early Paleozoic Bryozoa of the Baltic Provinces 368 



11. Early Paleozoic Bryozoa of the Baltic Provinces 370 



12. Early Paleozoic Bryozoa of the Baltic Provinces 372 



13. Early Paleozoic Bryozoa of the Baltic Provinces 374 



TEXT FIGURES. 



Page. 

 Fig. 1. Map of Baltic Sea area, showing distribution of Ordovician and Silu- 

 rian strata. (After von Schmidt.) 5 



2. Map of the North Polar region, showing distribution of Silurian strata 



in North America and northern Europe, with the hypothetical 

 shore lines. (After Weller.) 40 



3. Generalized paleogeographic map, showing supposed distribution of 



land and water during Black River and early Trenton times 43 



4. Bathymetric chart of the North Polar Seas, suggesting routes of 



migration for marine organisms . (After Nansen. ) 44 



5. Vinella repens. a, two colonies, natm-al size; &, portion of one of the 



colonies, X 18; c, another portion of same zoarium, X 18; c?, another 

 specimen, natural size, attached to a fragment of shell; e, email 

 portion of same, X 18. (After Ulrich.) 56 



6. Heteronema priscum. a, a colony attached to a valve of Obolus, 



X 4; 6, a portion of the same, X 20; c, parts of two colonies, X 35, 

 with one growing over another; d, small portion of another zoarium, 

 X 50 58 



7. Stomatopora arachnoidea. a, portion of a delicate zoarium, X 9; 



h, part of the same, X 20, illustrating the detailed structure 60 



8. Corynotrypa delicatula. Specimens figured by Ulrich as Stomato- 



pora proutana. a, fragment of a zoarium, X 9; & and c, two groups 



of zooecia, X 25; d, several zocecia of unusual size, X 25 62 



9. Corynotiypa barberi. a, portion of the type-specimen, X 9, incrust- 



ing a bifoliate bryozoan; h, several zooecia, X 20; c, part of a small 



colony, X 9, growing upon a species of Heliolites 63 



10. Corynotrypa inflata. a and h, zoarium, natural size, and a portion, 



X 9; c, three zocecia of same, X 18, showing the porous wall; d, 



a vertical section of a zooecium, X 18; e and/, small portion of a 



colony, incrusting Rafinesquina alternata, X 9 and X 18; g, out- 



- line of zocecia, X 18, showing three "gems" springing from one 



parent cell. (After Ukich.) . . . 65 



VII 



