FOSSILS OF THE NIAGARA GROUP. 425 



GENUS SPH^REXOCHUS, Beyrich. 

 ' Sph^rexochus romingeri, Hall. 



PLATE XXI, FIGS. 4-7. 



[ ' SphfBrexochus mirus, of authors; not S. mirus of Beyrich. 



SphcBrexochus romingeri, Hall. Geological Report of Wisconsin, p. 4.34. 1862. 

 SphcRrexochus mirus, Hall ; in Twentieth Rep. State Cab., 1st edit., p. 334. 1867. 



This species was at first supposed by me, to be identical with the S. 

 minis of Europe, but a farther careful study of it with larger collections 

 for comparison, has shown certain differences m the form and proportions 

 of the head, size of the cheek, etc., warranting its separation fi-om the 

 European species. The annulations on the axis of the pygidium are not 

 so abrupt, nor the posterior extension so great ; while the lateral lobes 

 are more free at their extremities, giving a very different aspect to this 

 part of the fossil. 



This fossil is pretty widely distributed, occurring at nearly all the 

 localities of the Niagara group in Wisconsin and Illinois. 



GENUS CALYMENE, Brongniart. 

 Calymene niagarensis. Hall. 



Calymene niagarensis. Hall. Geological Report, 4th District, N. T., p.^lOl, fig. 3. 

 Calymene blumenbachii var. niagarensis, Palaeontology of New York, vol. ii, p. 307. 



This species occurs in nearly all the localities of the Niagara group in 

 Wisconsin. Its most common condition is that of impressions of the 

 exterior crust, while casts of the interior are less frequently obtained. 



GENUS ENCRINURUS, Emmerich. 

 Encrinurus nereus, n. s. 



PLATE XXI, FIG. 15. 



Pygidium triangular ; length and breadth about equal. Axis sharply 

 elevated and marked by about eighteen rings, with a farther exten- 

 sion upon which no markings are distinguishable. The lateral lobes 

 are marked by eight or nine distinct costse, which, in the cast, are 

 not tuberculated. 



This species differs from the one in the Clinton group of New York, 

 in the greater number of ribs on the lateral lobes of the pygidium, while 

 there are fewer annulations on the middle lobe. 

 Cab. Nat. 54 



