378 REPORT ON THE STATE CABINET. 



Formation and Locality. — In limestone of the age of the Niagara group, 

 Racine, Wisconsin, and also in rocks of the same age at Waldron, Indiana. 



Spirifera gibbosa, Hall. 



PLATE XIII, FIGS. 6, 8. 

 Spirifer gibbosus, Hall. Rep. Progress GeoL Survey Wisconsin for 1860, p. 25. 1861. 



Shell somewhat below the medium size, gibbous ; beaks slightly incurved, 

 area less than the width of the shell below, about three times as 

 wide as high ; cardinal extremities rounded ; foramen large, higher 

 than wide ; valves marked by about four simple low rounded plica- 

 tions on each side of the mesial elevation. Dorsal valve extremely 

 gibbous on the umbo, regularly arcuate transversely ; mesial eleva- 

 tion broad, flattened above ; plications not extending to the beak. 

 Ventral valve deeper than the dorsal, but less arcuate ; mesial 

 depression broad and deep, rounded at bottom. Surface of both 

 valves (in well preserved specimens) show evidence of fine radiating 

 strias. 



This species resembles S. crispiis of the Niagara group in New York, 

 but is much larger, frequently more than twice as wide as that species ; 

 the mesial elevation is wider and not so high. The specimens described 

 are all internal casts, so that the external surface characters cannot be 

 fully given. 



Formation and Localitij. — In limestone of the age of the Niagara group, 

 Ptacine, Wisconsin. 



Spirifera plicatella, var. radiata, Sow. 



PLATE XIII, FIGS. 9-11; PLATE XXV, FIGS. 4-G. 



Spirifera plicatella, var. radiata, Sow., Delthyris lineatus (text), radiatus (index) : Sow. Min. 



Con., V, p. 493, figs. 1, 2. 1825 : not Anomia lineatus, Martin. 

 Spirifer radiatus, J. DeC , Sow. Silurian System, Plate xii, fig. 6. 1830. 

 Spirifer radiatus, M'Cor. Synopsis of tlie Silurian fossils of Ireland, p. 37. 1848. 

 Spirifer pticatellus, Salter; in Memoirs Geol. Survey of Great Britain, II, p. 328. 1848. 

 Spirifer cyrtmna, Davidson; in Bui. Soc. Geol. de France, 2d series, V, p. 324. 1848. 

 Spirifer radiatus. Hall. Pal. N. Y., II, pp. 66, 265, Plate xxii, fig. 3 ; Plate liv, fig. 6. 1852. 

 Spirifer plicatell'US, var. radiatus, S.vlter. Siluria, Plate ix, fig. 12; Plate xxii, fig. 7. 1859. 

 Spirifera plicatella, LiNBS4'«eM ; in Proc. Royal Acad, of Science of Stockholm, p. 358. 1860. 



It seems not worth while to risk the addition of another synonym for 

 any variety of this very variable species, but the Wisconsin specimens 

 commonly referred to it present some unusual characteristics. The form 

 is rhomboidal or transversely oval, and usually very gibbous. The car- 



