PALJEONTOLOG Y. 2 I 



are never much crowded, and hold no definite position in relation 

 to each other in the adjoining rows, sometimes found alternating, 

 sometimes opposite, or negligently disseminated. 

 \ External form of polyparia hemispherical, or discoid, lenticular, 

 with a concentrically wrinkled epithecal crust on the lower centrally 

 attached side. 



Occurs abundantly in the Niagara group of Drummond's Island, 

 Point Detour, and all along the south shore of the Upper Penin- 

 sula of Michigan ; also common in the drift deposits, and in the 

 Niagara group of Wisconsin, Iowa, etc. The above species descrip- 

 tion comprises specimens so much differing in aspect, that it seems 

 strange to present them as belonging to one species. A Favosites 

 with tubes six millimeters wide and one with tubes measuring 

 only two are in great contrast. It may be said also that specimens 

 with convex diaphragms and rough spinulose tube walls bear little 

 resemblance to others having perfectly even diaphragms and almost 

 smooth tube cavities ; yet on careful examination of large collec- 

 tions of these forms, we find them all so much linked together by 

 intermediate gradations that no line can be drawn between one 

 and another. 



Plate IV. represents four specimens, which I consider as varie- 

 ties of Favos. favosus. Fig. i is the fragment of a large silicified 

 specimen with tubes about four or five millimeters in width, flat 

 diaphragms with numerous marginal depressions, and with deli- 

 cately spinulose tube walls. Found at Drummond's Island. Fig. 2 

 is a specimen from Point Detour, with still larger tubes of simi- 

 lar structure. The edges of the cells are noticed in the figure to 

 be faintly crenulated by the twelve longitudinal furrows. Figs. 

 3 and 4 are specimens with convex diaphragms, of different tube 

 size, with well-developed marginal depressions ; surface of dia- 

 phragms and inner face of tube walls spinulose. Found associated 

 with the former. 



Plate V. — Fig. 2 is a specimen fully agreeing with Fig. i , Plate IV., 

 but of smaller tube size. Favosites Gothlandica, of Goldfuss, cor- 

 responds with this specimen ; Favosites Niagarensis, Hall, includes 

 forms of this kind also, but the name Gothlandica is applied to so 

 many entirely different forms of Favosites, that I totally abstain 

 from using it. The name Niagarensis, Hall, I have restricted to a 

 form with smaller tubes. 



