PLATE VI. 
All the figurers on this plate except No. 18 are X18. 
RASS SIO 2ianGs Lo. RAEN ED LO DAN NTO DA Tats ml Merpaletets tolalolejereleisiofeteler={-lelal=jateie[everstaleiaplstalclateleleioeietateye 125 
1. Tangential section of an old and thick example of the usual form of this species. Figs. 
6 and 12 represent transverse and vertical sections of same. 
2and 38. Tangential and vertical sections of a fragment of the var. SENILIS (see p. 127), 
showing the great abundance of the median tubuli and the structure of one of the 
solid spots. 
4and5. Tangential and vertical sections of a well preserved and typical example. 
6. Small portion of a transverse section prepared from the same specimen that furnished 
the originals of figs. 1 and 12. 
12. Vertical section of a thick specimen. (See figs. 1 and 6). Only one side of the zoarium 
is entirely represented. 
13. Tangential section of a young example. 
For the external characters of this species see plate VII. 
Middle third of the Trenton shales at Minneapolis and St. Paul. 
TS e er eANG Saye LVELLEN ELD CD Weta GROUT ROTTS aU) lite aye iene stelaystetnpete) lel attate(sfuteratelals]stctatatataent=teleitetste <lst-tata oleetayerstele orate 134 
7. Tangential section, showing structure immediately beneath the surface; 7a, small por- 
tion of same section showing appearances at the bottom of the vestibular region; 7b, 
another portion of same, showing the form of the primitive portion of the zomcia and 
the minutely tubular character of the walls and mesial lamin. 
8. Vertical section of same specimen, showing well developed superior hemisepta. 
Middle third of the Trenton shales at Minneapolis. 4 
Figs. 9to11. EURYDICTYA MULTIPORA Hall (?)......-..--.---.--.--- er AE ALATA etre tetera Mer aleve eeeje saver 139 
Tangential, transverse, and vertical sections of a narrow frond from the upper third of 
the Trenton shales at St. Paul. (See also plates VII and XIV.) 
Figs. 14 to 18. RHUNIDICTYA TRENTONENSIS Ult...... 0.020 ee ee cece c eee eee e ence eee cere een e ee sb} 
14and 15. Transverse and vertical sections of a young example. 
16and 17. Vertical and tangential sections of a thicker specimen. In this each side is in 
part composed of two distinct layers of zocecia. 
18. Primitive or prostrate portion of one zocecium of fig. 16, more highly magnified (50). 
See also plate VII. 
Lower third of the Trenton shales, Minneapolis, Minn. 
Figs. 19 and 20. RHINIDICTYA GRANDIS, D. SP......- esse eee eee eee eet eee ih cece iy oN te 136 
Vertical and tangential sections of a specimen from the ‘‘Lower Blue” limestone at 
Dixon, Ill. 
