The Relationship of the Tetracoralla to the Hexacoralla. 167 



List of Species. 



Microcyathus cyclosfoma (Phillips). Genotype. 



Hydnoporaf cyclostoma Phillips. Geology of Yorkshire, Pt. 



2, Mountain Limestone Dist., 1836: 202. 

 Locality and horizon: Western Europe. Lower Carboniferous. 

 Microcyathus enormis (Meek and Worthen). 



Sphenopoterium enornie Meek and Worthen. Proc. Acad. 



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

 Locality and horizon : Rockford, Indiana; Clarksville, Mis- 

 souri. Mississippian (Kinderhook). 

 Microcyathus? antiquus (McCoy). 



Astrceopora antiqua McCoy, Synop. Carb. Limestone Foss. 



Ireland, 1862: 191. 

 Locality and horizon: Ireland. Lower Carboniferous. 

 Remarks: This species has been considered to be identical with 

 M. cyclostoma, but Hinde examined specimens from the type 

 locality and decided that they were distinct. He even sug- 

 gested that they may be placed in a distinct genus. 

 Microcyathus depressus (Meek and Worthen). 



Sphenopoterium enorme var. depressum Meek and Worthen. 



Geol. Surv. 111., Vol. II, 1866 : 146. 

 Locality and horizon: Monroe County (Salt Lick Point), Illi- 

 nois; Missouri. Mississippian (Fern Glen). 

 Microcyathus koninckii (Etheridge and Nicholson). 



Paloeacis cyclostoma var. koninckii Etheridge and Nicholson. 



Ann. Mag. Nat. Hist, Ser. 5, Vol. I, 1878:224. 

 Locality and Jiorizon: Western Europe. Lower Carboniferous. 

 Microcyathus bifidus (Weller). 



PalcEacis bifidus Weller. Bull. Geol. Soc. America, Vol. XX, 



1909:277. 

 Locality and horizon: Missouri and Illinois. Mississippian 

 (Fern Glen). 



Genus Ptychochartocyathus Ludwig. 



1866 Ptychochartocyathus Ludwig. Palaontographica, Vol. 

 XIV: 231. 



The genus was not defined and the figures are not definitive, 

 but apparently this group differs from Palceacis in having well 

 defined spines on the inside of the cup, no pores, and a basal 



