666 



NORTH AMERICAN INDEX FOSSILS. 



192. M. (Maclurina*) manitobaensis Whiteaves. (Fig. 921.) 



Ordovicic. 

 Maximum diameter S}4 inches, proportionately low, whorls 



Fig. 920. Maclurea logani, X %> Young with operculum in place ; operculum of 

 adult ; umbilical view of first specimen. (After Salter, Can. Org. Rem., I. ) 



slowly increasing in diameter; umbilicus moderate; upper side 

 with periodic growth constrictions. 



Fig. 921. Maclurea {Maclurina) manitobaensis, X %• (After Ulrich, Pal. Minn.) 



Trenton of Minnesota and numerous localities in Manitoba and 

 elsewhere. 



193. M. (Maclurina) cuneata Whitf. (Fig. 922.) Ordovicic. 



Fig. 922. Maclurea [Maclurina) cuneata, X %> (After Ulrich, Pal. Minn.) 



* Maclurina is separated from Maclurea by Ulrich and Scofield on account of the 

 absence of the muscular projections on the inside of the operculum characteristic of the 

 true Maclurea (see Fig. 920). 



