1 66 IV. I. Robinson, 



PalcBacis obfusa (Meek and Worthen). 



Sphenopoterium obtusum Meek and Worthen. Proc. Acad. 

 Nat. Sci. Phila., Vol. XII, i860, 1861 : 448. 



Palceacis cymba Seebach. Zeit. deutsch. geol. GeselL, Vol. 

 XVIII, 1866:309. 



Palceacis mnbonata Seebach. Ibid., Vol. XVIII, 1866:309. 



Locality and horizon: Nauvoo, Illinois. Mississippian (Keo- 

 kuk). 

 Palceacis compressa (Meek and Worthen). 



Sphenopoterium compressum Meek and Worthen. Proc. Acad. 

 Nat. Sci. Phila., Vol. XII, i860, 1861 : 448. 



Locality and horizon: Nauvoo, Illinois. Mississippian (Keo- 

 kuk). 

 Palceacis cavernosa Miller. 



Adv. sheets, 17th Ann. Rep. Geol. Surv. Ind., 1891:4. 



Locality and horizon: Jackson County, Indiana. Mississippian 

 (Waverly). 

 Palceacis carinata Girty. 



Ann. N. Y. Acad. Sci., Vol. XX, No. 2, Pt. 2, 1910: 190. 



Locality and horizon: Arkansas. Mississippian ( Fayette ville 

 shales). 



Genus Microcyathus Hinde. 



1896 Microcyathus Hinde. Quart. Jour. Geol. Soc, London, 

 Vol. LII : 447. 



Hinde suggested that a new genus be based upon Hydnopora? 

 cyclostoma Phillips. It is here proposed to extend the genus to 

 several other forms. Specimens of the genotype have not been 

 accessible, but it is believed to be definitely related to the species 

 listed below. The genus may be defined as follows : 



Leptoporidse, sometimes attached but often without a trace 

 of attachment scars. Shape roughly spheroidal. \\'alls very 

 thick; composed of contorted lamellae pierced by ramifying 

 canals. Pores, communicating with the canals, lining the steep 

 walls of the inner cavity. Calices with broad, almost flat, floors. 

 Number of corallites seldom more than three. 



This genus differs from Palceacis in the microstructure, the 

 external shape, and the cup-shaped or almost cylindrical instead 

 of conical cavities. 



