PLATE VII. 
HIS ETO IOS SEVELEN TDI CUveAm PHI EC [le AUT A uaMeS  sieyeteteleyeteletraletatsclcrelsrs. oie: tetnict =Joseie\aje?e eecretenaisisneyers ated terete yar terse 
1to4. Four specimens of the natural size, showing the mode of growth prevailing in this 
species. Three of the specimens preserve the footstalk. 
5. Surface of a slightly weathered example <9. In better preserved examples the nonpori- 
ferous margins are much wider. (See description.) 
Lower limestone of the Trenton formation, Minneapolis, Minn. 
Migs 60/9. RHINTDLODP YA REN TONMNGIS Ait ners fetetecte coiieisieeracteele erciarsieleraines sehctal lass ove rein picienetetateteiore 
6to8. Three fragments of the natural size. 
9. A well preserved fragment of the natural size and x9. (See also plate VI.) 
Lower third of the Trenton shales, Minneapolis, Minn. 
IDES KO) a) Mase HaNel tsa PA —)isvonpGo you AN ai nopW ati OupIs} Oflliene or ana ognscoen Goeane Donn sASobhoaemeaanoste 
10. Surface of an old and excellently preserved fragment, x9. 
11 to 14. Four representative specimens of the natural size. The original of fig. 11 belongs 
to the Survey Museum; Reg. No. 5939. It is from the upper third of the Trenton shales 
at St. Paul. 
15. Portion of original of fig. 13, x9, illustrating the appearance of a large number of 
specimens. 
18. A finely preserved fragment, natural size and a portion <9. In this specimen the 
zowcia are unusually small. 
19 to 21. A very young specimen (var. minor of my preliminary report,) natural size, a por- 
tion <9, and several zocecial apertures *35. The margins are wide and sharp, the 
_outer zooscial apertures large and oblique, and the walls in the central part very 
delicately granulose. (See also plates VI and VIII.) 
Middle third of the Trenton shales, Minneapolis and St. Paul, Minn. 
Figs. 16 and 17. RHINIDICTYA MUTABILIS, var. SENILIS, n. var 
A specimen of the natural size and a portion <9. 
Middle third of the Trenton shales, St. Paul, Minn. 
Figs. GA =) 25 to 28, and 32. RHINIDICTYA MALTABILIS, Var. MAJOR Ulr......-..-....5--2 2. - see 
2and 23. A well preserved but narrow stipe of this variety of the natural size, and a few 
zowcial apertures, with a portion of oneof the solid spots or macule, <18. 
25 to 28. Four specimens of the natural size. 
32. Small portion of the surface of the original of fig. 28, x9. (See also plate VI.) 
Middle third of the Trenton shales, St. Paul and Minneapolis. 
Wigs2+-and 29tols UR Y DICTA Mn UTEIPOR ANGE alll)inseisenscemeeieecincaee een ee eeees 
24 and 30. A narrow, parallel-margined example of the natural size and a portion x9. This 
resembles Rhinidictya mutabilis, var. major to such a degree that it was at first regarded 
as belonging to that variety. 
29 and 31. A small, irregularly divided frond, natural size and a portion x9. This spec- 
imen is evidently young, being thin and but inconspicuously maculose. (See also 
plates VI. and XIV.) 
Upper third of the Trenton shales at St. Paul, Minn. 
127 
139 
