THE FRONT OF THE FHOCESSION OF LIFE. 79 



from the whole extent of the typical region of the Pots- 

 dam sandstone. These have been named Lingula prima 

 and Lingula antiqua. They are 

 little bivalve shells belonging at 

 the bottom of the class Brachio- 

 poda, which is nearly the lowest 

 class among molluscs. As desti- 

 Fig. 23. Lingula Fig. 24. Lingula tute of the senses as an oyster, 



prima. antiqua. , ,, , . n 



they were equally incapable 01 

 locomotion, being anchored to the bottom by a fleshy 

 stem or peduncle which issued through the hinder part of 

 the shell, and had an internal organization which was even 

 more rudimentary and homogeneous than that of the " bi- 

 valve," which has become the type of insensibility and 

 stupidity. The same little shells have been observed in 

 Northern Michigan, in Minnesota, in 

 Wisconsin, in Alabama, and even in 

 the Old World, every where occupy- 

 ing a position in strata w T hich were 

 accumulated at the same time as the 

 Potsdam sandstone. In many in- 

 stances the extent to which the 

 number of individuals was multi- 

 plied is truly amazing, while the 



Whole Catalogue of Species of mol- Fig . 25. Modern Lin gnlas an. 



luscs in this sandstone scarcely chorea to a support, 

 reaches half a dozen. With these bivalves, in Wisconsin 

 and Minnesota, are associated incredible numbers of trilo- 

 bites. As might be expected in deposits formed under 

 such conditions as gave rise to sands, the trilobites are 

 found generally in a greatly damaged condition. These 

 Northwestern cemeteries have been mainly explored by 

 Dr. D. D. Owen, Professor James Hall, and Dr. B. F. Shii- 

 mard. The writer has also had the opportunity to bring 



