PLATE F. 



PAGE. 

 Figs. 1 to 4. RECEPTACULITES OWENI Hall 57 



1. The upper or inner surface of a large fragment. Mineola, Minnesota. 



2. A portion of the under surface of a specimen in which the head plates are sur- 



mounted by a knob-like projection. Twelve miles south of Cannon Falls, Minn. 



3. A small portion of a large specimen in which are shown twelve radiating canals 



in each depression left by the spicular head plates. 



4. Another portion of the same specimen in which the casts of the radiating canals 



are removed, leaving the clay fillings between the head plates serrated. Galena 

 shales near Fountain, Minn. Minnesota Geological Survey collection. 



Figs. 5 and 6. ISCHADITES IOWENSIS Owen, sp 64 



View of the under surface and profile of the same specimen, a natural cast of the 



spaces left between the vertical rays of the spicules. Galena, Wasioja, Dodge 



county, Minn. Minnesota Geological Survey collection. 

 Figs. 7 to 10. ISCHADITES KXENIGII Murchison 61 



7. "The base of Ischadites kcenigii Murchison, enlarged three times, showing the 



eight diamond-shaped spicular plates of the nucleus and the plates succeeding 

 them, each having a clearly marked central spot, indicating the center of the 

 spicule." (After Hinde.) 



8. "A portion of the lateral surface of a specimen, enlarged four times, showing 



the extension of one of the horizontal rays of each spicule, from beneath the 

 distal angle of the correspoding-summit plate, over the summit plate of the 

 spicule in front of it. In the center of the figure are the modified summit- 

 plates developed at the intercalation of a fresh row of spicules." (After Hinde.) 

 9 and 10. "Portion of the lateral areas of two specimens, in which the surface summit- 

 plates have disappeared, showing the four horizontal rays of independent 

 spicules. The rays are often incomplete, and they frequently overlap each 

 other. Enlarged three times." (After Hinde.) 



Figs. II and 12. LEPIDOLITES DICKHAUTI Ulrich* 67 



11 . Surface of a specimen x 10, showing the imbricating character of the head plates. 



12. View of the inner side of the integument of another specimen, x 10. Lower part 



of the Cincinnati group, Covington, Ky. Collection of E. O. Ulrich. 



Figs. 13 to 15. ANOMALOSPONGIA RETICULATA Ulrich 69 



13. A compressed-conical fragment of the natural size. 



14. Surface of a well preserved fragment x 18, showing the character and arrange- 



ment of the spicules. 



15. Diagrammatic view of one of the spicules x 18. Cincinnati group, Covington, 



Ky. Collection of E. O. Ulrich. 



Figs. 16 to 18. RAUFFELLA FILOSA Ulrich 75 



16. View of an average specimen of the natural size. 



17 and 18. Small parts of the surface of two specimens x 4, showing variable appearance of 

 the spicular network. Middle third of the Trenton shales, St. Paul, and Min- 

 neapolis. Collection of E. O. Ulrich. 



Figs. 19 and 20. RAUFFELLA PALMIPES Ulrich - 76 



19. Small specimen with the radial leaves mostly broken away; natural size. Mid- 



dle third 01 the Trenton shales, Minneapolis. Geological Survey collection. 



20. Surface (x 9) of a well preserved specimen in the collection of E. O. Ulrich. Shows 



the hirsute appearance of the external spicule layer. 



Figs. 21 to 23. SOLENOPERA COMPACTA Billings 80 



21. A figure of a small mass. Trenton shales near Cannon Falls, Minn. Minnesota 



Geological Survey collection. 

 22 and 23. A longitudinal and transverse section x about 50. (After Nicholson.) 



The drawings for figures 11 to 20 are by Mr. Ulrich. 



