RES eel toe 
il 
2. 
‘Oe 
4. 
Figs. 5and 6. 
Figs. 7 to 10. 
tte 
8. 
9 and 10. 
Figs. 11 and 12. 
INANE 
12. 
Figs. 13 to 15. 
13. 
14. 
15. 
Figs. 16 to 18. 
16. 
17 and 18. 
Figs. 19 and 20. 
19. 
20. 
Figs. 21 to 23. 
22 and 23. 
PLATE F. 
Fool WNOL OH Gso Oy Awcel ISNILS Gaboooeasdons. conn sceoan ponddoo on aachaoros0soq0008 
The upper or inner surface of a large fragment. Mineola, Minnesota. 
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. 
A small portion of a large specimen in which are shown twelve radiating canals 
in each depression left by the spicular head plates. 
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. 
TSCHADILES LOW NSISh OW EU SIS Diets cays rererer (el ametstetoretedala)atel-tereleretelictalerelalebatetelereteteieaetelstoters 
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. 
TSCGHADUDHS KGENEGHT VIC M1 SOM rteretoretercie!elatolelafaleicteperete ters areloleleteeietatatst=ieietttetetsveleteneieiereiars 
“The base of Ischadites keenigii 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.) 
‘‘ 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.) 
‘Portion of the lateral areas of two specimens, in which the surface summit- 
pilates bave 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.) 
HEPIDOLULES DIORA DI: WUTC scare erate eystaiel ote ei aisielsverele lols nlevevoinieiorereeiararetsieleleebaie aetelets 
Surface of a specimen 10, showing the imbricating character of the head plates. 
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. 
ANOMATOSPONGIAGREDICUIAIA (Mliri Chita eeraieleialeinie let ioriels/ereivtelsteieieieieieteieisisielertrielster= 
A compressed-conical fragment of the natural size. 
Surface of a well preserved fragment x 18, showing the character and arrange- 
ment of the spicules. 
Diagrammatic view of one of the spicules x 18. Cincinnati group, Covington, 
Ky. Collection of E. O. Ulrich. 
LRVALOIAN OIG Cy WI AOU Oh Masa rnoraooonmanooscce odoannuoaasdaodouobs doccnacacmoD0Nns 
View of an average specimen of the natural size. 
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. 
UATE CAs ACE MITETES I UIT Ch avetatateratarenerapetevete ciayioln sie ressuercieler-rletenstmeetstetchtalieveretare)/aleysccielaiete 
Small specimen with the radial leaves mostly broken away; natural size. Mid- 
dle third 01 the Trenton shales, Minneapolis. Geological Survey collection. 
Surface (x 9) of a well preserved specimen in the collection of E. O. Ulrich. Shows 
the hirsute appearance of the external spicule layer. 
SOLENOPERAy COMPACTAS Bilin SStrercemteec -tieeticieteteristeiectetrtekcieereReeieicintstateiatstarsietete 
A figure of asmall mass. Trenton shales near Cannon Falls, Minn. Minnesota 
Geological Survey collection. 
A longitudinal and transverse section x about 50. (After Nicholson.) 
*The drawings for figures 11 to 20 are by Mr. Ulrich. 
64 
61 
76 
80 
