PLATE III. 



Page 



Figs. 1 to 3. Helopora divaricata Ulr 19: 



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



2. Portion of same, xl8. Only three of the four rows of zooecia to be seen in this view have 



been drawn. . j, j.^. • 



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

 Lower third of the Trenton shales at Minneapolis, Minn. 



Figs. 4 to 6. Helopoea spinifokmis Ulr 19' 



4. A segment natural size, and lower portion of same xi8. 

 5 and 6. Vertical and transverse sections, xi8. 



"Glade" limestone at Lavergue, Tenn. 

 Fig. 7. Aethboclbma armatum Ulr • ■; ,.• •••■>; ^^ 



A small segment supposed to belong to the tertiary set of this species, xi8. Cannon 

 Falls, Minn. (See also plate II.) 

 Fig. 8. Helopora (?) sp. undet ■ • • ^WW- ^^' 



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



Fig. 9. Helopora alternata Ulr v • • ;v-.:,v,' • 'A'-' i" ' "i" V^: ' m' ' ' V ' ' ^®' 



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

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

 belong to the tertiary set of Arthroclema striatum Ulr. 



Fig. 10. Helopora mtjcronata Ulr ^•■"r;,:' : ^^ 



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 Arthroclema armatum Ulr. 

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



Figs. 11 to 12. Helopora hIrrisi James 19' 



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

 11a. Portion of original of flg. 11, x50. 

 116. Transverse section of a segment, X50. 

 Hudson River group, Waynesville, Ohio. 

 Figs. 13 and 14. Arthrostlus conjuncttts Ulr 181 



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



14. View of small portion of non-celluliferous side of same, xi8. 

 Trenton shales, near Fountain. Minn. 



Figs. 15 and 16. Arthrostyltjs obliqtjus Ulr 18( 



Two views of a segment of this species, xi8, in the first showing the non-ceUuliferous 

 side with the upper extremity and abojat 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. tenuis (James), from the lower 

 part of the rocks at Cincinnati, Ohio, 

 Figs. 17 to 20. Nematopora grajtosa Ulr ; 20 



17. Portion of unbranched fragment, xi8, showing the granulose angles and interspaces, 

 ; and narrow zooecial apertures; the latter in five rows. 



18. Bifurcating fragment, xi8, with the rows of granules slightly flexuous. 



19 and 20. Portion of slightly worn fragment, and end view of same, xi8. This has only 

 four rows of zooecia. 

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



Figs. 21 to 23. Nbmatopora conferta Ulr 20 



Zoarium of this species, natural size, xg, and portion of same xi8. Upper part of Galena 

 shales, near Cannon Falls, Minn. 



Figs. 24 and 25. Nematopora ovalis Ulr 20 



Two fragments of this opecies, natural size and xi8, the first with four rows of zooecia, 

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



Figs. 26 and 27 Nematopora delicatula Ulr 20 



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

 X18. Upper part of Galena shales, near Cannon Falls, Minn. 

 Figs. 28 to 33. Arthroclema striatum, n. sp 19 



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



ends. 



29. Lower end of same, xi8, 



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

 size and xi8. 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 xi8. One has five cycles of 

 zooecia 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 20 



View of upper end of the segment represented by fig. 18 on plate II; xi8. 



Figs. 35 to 37. Arthroclema, sp. undet t 20 



35. Slightly abraded segment, natural size and xi8. An obscure, subcentrally situated, 



articula-ting socket is distinguishable. 

 36 and 37. Two internal casts of the zooecia, xi8, showing their spiral arrangement in the 

 segments. 

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



