478 



HISTORICAL GEOLOGY. 



The peculiar markings, obliquely furrowed from a medial line named 

 Cruziana similis, by Billings, have been supposed to be plants, but are now- 

 regarded as the tracks of worms or some other animal (Fig. 567). 



3. Brachiopods. — The following are figures of a few species : — 



668. 



568-573. 



572. 



Brachiopods. — Fig. 568, Lingulepls antiqua (1); 569, 570, Lingulella prima (1); 571, 572, Obolella polita (1) ; 

 573, Tiiplesia (Camarella ?) primordialis. Fig. 568-570, Hall; 571, 572, Meek ; 573, Walcott. 



The Liiigulids are so abundant in some places that they give the beds a 

 shaly structure. 



4. Pteropods. — Fig. 574 is a HyoUthes, from the Big Horn Mountains. 

 Fig. 575 is a peculiar, rather thick, conical shell, doubtfully referred by 

 Walcott to the Pteropods. It is oval below in outline, and has an opercu- 

 lum like that of Hyolithes. 



5. Gastropods. — The Gastropods here figured (Figs. 578-582) pertain to 

 genera that, like Platyceras of the Lower Cambrian, are characteristic emi- 

 nently of more or less of later Paleozoic time. Bellerophon has the shell 



574-582. 



579. 



581. 



574. 



Pteropods. — Fig. 574, HyolitheBgregarius (1); 575, Matheria variabilis, lateral view (3) ; 576, 577, Bame, end 

 views of different specimens (1). Gastropods. — Fig. 578, Holopea Sweeti; 579, 580, Ophileta primor- 

 dialis; 581, 582, Bellerophon antiquatus. Fig. 574, from Meek; 575-577, Walcott; 578-582, Whitfield, 

 Wisconsin G. Rep. 



coiled in a plane ; it has also (but not shown here) a narrow slit in the lip 

 of the shell at its middle. B. antiquatiis^hiti., first described from Wis- 

 consin beds (Fig. 581), occurs also in Eureka, Nev. 



6. Trilobites. — Fig. 583 represents, reduced, one of the large species of 

 Dicellocephalus of Owen, from Minnesota, — the real length being six inches. 

 Figs. 585 and 585 a are head and pygidium of one of the small species 



'ft 



