

LOWER SILURIAN. 



177 



Fig. 261. 



1. Plants. 

 Two species of the genus of Fucoids, Pakeophycus, from Straits of Belle Isle, have 

 been described by Billings, as P. incipiens and P. congreyatus ; and the first of these 

 occurs also near S wanton, Yt. 



2. Animals. 

 Protozoans. — Sponges. —Fig. 261, Archceocyathus Atlanticus B., from the Straits 

 of Belle Isle : a, external form, diminished one- 

 half ; b, a polished transverse section, natural 

 size, showing an irregularity of structure, 

 like that of a sponge; Archasocyathellus Rens- 

 selaericus Ford, at Troy. 



The Green Sand of the Wisconsin and Ten- 

 nessee beds suggests the probable existence of 

 Bhizopods, since the shells of these Protozoans 

 have been found to be connected with the 

 origin of this material in the Silurian rocks of 

 Europe, as well as in those of the Cretaceous 

 in Europe and America. 



Radiates, —a. Polyps. —None are known. 



b. Acalephs. — Yigs. 270, 271, Dendrograms Hallianus, from St. Croix, Minnesota. 



Figs. 262-271. 

 26 VX oaa n 264 



Archaeocvathus Atlanticus. 



Figs. 262, 263, Linguleila prima: 264, L antiqua; 265, Scolithus linearis ; 266, 267, Conocorypha 



minuta, head and tail shields (x4); 268, Dicellocephalus Minnesotensis (XX); 269, C. 



Iowensis; 270, 271, Dendrograptus Hallianus. 



c. Echinoderms. — Stems of Crinoids, at La Grange, Minnesota (probably Cysti- 

 dean); and a single disk at Keeseville, N. Y. 



Mollusks a. Bryozoans. — None are known. 



b. Brachiopods. — Fig. 262, Linguleila (formerly Lingula) prima Conrad, from 

 Keeseville, N. Y. ; 263, same, from Lake Superior (Tequamenon Bay), and from St. 

 Croix. Wis.; 264. L. antiqua H. (or L. acuminata Conrad), from St. Croix, —a much 

 larger specimen than those of New York, but varying much in size and form. It is 

 common also in Canada. Other Lingulce occur in 

 Wisconsin and Canada. Obolella ? polita Hall (Obolus 

 Apollinis Owen) from near the mouth of Black River 

 in Iowa. Species of Obnldla have been described 

 from Trov, X. Y., and AVisconsin, and one (0. nana, 

 Fitrs. 272, 273), from the Black Hills of Dakota; 

 Obolus Labradoricus B, Straits Belle Isle; Obolella 

 chromntica B., ib. ; Obolella [Kutnrgina) cingulata B. 

 (recently shown to be 0. Phillipsii Salter, of mid- 

 dle Linjrula flags of Great Britain); 0. desqua- 

 nata Hall, and other species, Troy; Camerella antiquata B., Swanton; Orthisina 

 12 



Figs. 272, 273. 



Obolella nana. 



