PLATE III. 



PAGE. 



Pigs. 1 to 3. HELOPOBA DIVAKICATA Ulr 191 



1. A segment of the natural size and X7, Minneapolis. Minn. 



'2. Portion of same, x!8. Only three of the four rows of zocecia to be seen in this view have 

 been drawn. 



3. Transeverse section, xi8, showing a spiral development of the zocecia. 

 Lower third of the Trenton shales at Minneapolis, Minn. 



Pigs. 4 to 6. HELOPORA SPINIFORMIS Ulr 190 



4. A segment natural size, and lower portion of same xis. 

 5 and 6. Vertical and transverse sections, xis. 



"Glade" limestone at Lavergue, Tenn. 



Pig. 7. ARTHROCLEMA ARMATUM Ulr 201 



A small segment supposed to belong to the tertiary set of this species, xis. Cannon 

 Palls, Minn. (See also plate II.) 



Fig. 8. HELOPORA (?) sp. undet 196 



Nearly entire segment, xi8. Upper part of Galena shales, near Cannon Falls, Minn. 



Fig. 9. HELOPORA ALTERNATA Ulr 192 



About three fourths of a segment of this species, xis. Middle third of the Trenton 

 shales, Minneapolis, Minn. It is within the possibilities that these segments may 

 belong to the tertiary set of Arthrockma striaturn Ulr. 



Fig. 10. HELOPOEA MUCRONATA Ulr 193 



A segment of this form natural size, and the greater part of it xi8. The specimens 



upon which this species is found may prove to belong to Arthrockma armatum Ulr. 

 Upper part of Galena shales, near Cannon Falls, Minn. 



Figs. 11 to 12. HELOPORA HARRISI James 195 



11 and 12. Two segments, natural size and xi8. 

 llct. Portion of original of fig. 11, X50. 

 lib. Transverse section of a segment, X5q. 



Hudson River group, Waynesville, Ohio. 

 Figs. 13 and 14. ARTHROSYLUS CONJUNCTUS Ulr 188 



13. Lateral view of the central portion of a segment, -18. 



14. View of small portion of non-celluliferous side of same, xis. 

 Trenton shales, near Fountain, Minn. 



Pigs. 15 and 16. ARTHROSTYLUS OBLIQUUS Ulr 188 



Two views of a segment of this species, xis, in the first showing the non-celluliferous 

 side with the upper extremity and about three-fourths of the length, in the second 

 the central portion turned so as to show the lateral aspect. 

 Lower third of the Trenton shales at Minneapolis, Minn. 



Beneath fig. 15 a small figure is erroneously marked with the number 16. This repre- 

 sents a transverse section of the type of the genus A. tennis (James), from the lower 

 part of the rocks at Cincinnati, Ohio. 

 Figs. 17 to 20. NEMATOPORA GRANOSA Ulr 205 



17. Portion of unbranched fragment, xis, showing the granulose angles and interspaces, - 



and narrow zorecial apertures; the latter in five rows. 



18. Bifurcating fragment, xis, with the rows of granules slightly flexuous. 



19 and 20. Portion of slightly worn fragment, and end view of same, xis. This has only 



four rows of zocecia. 

 Upper part of Galena shales, near Cannon Falls, Minn. 



Figs. 21 to 23. NEMATOPORA CONFERTA Ulr 206 



Zoarium of this species, natural size, xg, and portion of same xis. Upper part of Galena 

 shales, near Cannon Falls, Minn. 



Figs. 24 and 25. NEMATOFORA OVALIS Ulr 204 



Two fragments of this opecies, natural size and xis, the first with four rows of zooacia, 

 the other with five. Upper part of Galena shales, near Cannon Falls, Minn. 



Figs. 26 and 27 NEMATOPORA DELICATULA Ulr 206 



Two fragments of the exceedingly delicate zoarium of this species, natural size and 



xis. Upper part of Galena shales, near Cannon Falls, Minn. 

 Figs. 28 to 33. ARTHROCLEMA STRIA TUM, n. sp 198 



28. Primary segment, natural size and xi2, with a large articulating socket and expanding 



ends. 



29. Lower end of same, xjs. 



30 and 31. Lateral and end views of a large and strongly striated primary segment, natural 

 size and xis. The zooecial apertures are incorrectly represented in this figure. (See 

 correction p. 199, sixth line from top.) 



32 and 33. Two segments of the secondary set, natural size and xis. One has five cycles of 

 zooacia and an articulating socket, the other six cycles and no distinguishable socket. 

 (See also plate II.) 

 Middle third of the Trenton shales, Minneapolis, Minn. 



Fig. 34. ARTHROCLEMA CORNUTUM Ulr 200 



View of upper end of the segment represented by fig. 18 on plate II; xis. 



Figs. 35 to 37. ARTHROCLEMA, sp. undet 203 



35. Slightly abraded segment, natural size and xis. An obscure, subceotrally situated, 



articulating socket is distinguishable. 

 36 and 37. Two internal casts of the zooecia, xis, showing their spiral arrangement in the 



segments. 

 Upper third of the Trenton shales, St. Paul, Minn. 



