24 Cincinnati Society of Natwal History. 



haps, it ought not to be separated. The species united above are all 

 too indefinite in character to be recognizable, so they are all re 

 duced to synonyms. In one the calices are arranged more or less 

 regularly. 



Formation and Locality. — Lower Silurian, Cincinnati Group. 

 Cincinnati and Hamilton, O., etc. 



46. — M. wETHERBVi, Ulrich. 



Jour. Cin. Soc. N. Hist., V. 239, 1882; 14th Ann. Rept. 

 (;eol. & N. H. .Soc. Minn , 129, 1886. 



Corallum forming a thin, irregular e.xpansion on \arious for- 

 eign bodies, with the center sometimes slightly elevated. Surface 

 sometimes nearly smooth, but often raised into low monticules, 

 which are occupied by larger c:ells ; in the nearly smooth forms 

 these occupy patches scattered irregularly over the surface. Cal- 

 ices polygonal, with thin walls. Prominent spiniform corallites 

 occupy the angles of the cells in well preserved specimens. 



var. ASPERULA, Ulrich. 



Petigopora asprrn/a, Ul. Ibid, VI, 157. 1883; i4lh Rept. G. 

 & N. H. Sur. Minn., 130, 1886. 



Differs from the type merely in being sub-circular in outline, 

 and being generally attached to the shells of Strophemena altcrnata. 

 It approaches quite closely to M. petechialis, Nich., but differs in 

 being larger and having more prominent monticules. 



Obs. — In this species and variety we have an example ot what 

 is spoken of under M. petechialis, Nich., namely, that probably the 

 smaller forms are merely the younger individuals. The close re- 

 semblance between this species and its variety would seem to indi- 

 cate the truth of the idea. In both the monticules are only slightly 

 raised, and have larger cells than the average. Both have num- 

 bers of spiniform corallites, and both are found at the same horizon. 



Formation and Locality. — Type torm, Lower Silurian, I'renton 

 (iroup at High Bridge, Ky., and Chazy (?) Group at Minneai)olis. 

 Minn. Variety, Trenton Group, Minneola, Minn., Cincinnati 

 Group, Cincinnati, O. 



47. — M. PETECHIALIS, Nicholson. 



C/urtctes petec/iialis, Nich., Pal. Ohio II, 213, 1875. 



Petigopora petechialis, Ulrich. Jour. Cin. S. N. Hist., VL 156, 

 1883; 14th Rept. Geol. & N. H. Sur. Minn., 103, 1886. 



Corallum forming small circular patches, from less than one- 

 half a line to a line and one-half in diameter, attached parasitically 



