NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA — GRANT 43 



Table 1. — Measurements of Atribonium simatum from Nezvton Creek Limestone , 

 quarry of Michigan Alkali Co., Alpena, Mich. 



Measurements, in millimeters 



Shale in size, but differs in its more trigonal outline with flat or emar- 

 ginate anterior, more numerous costae on the fold, greater thickness, 

 weaker costae, and less prominent fold. It differs from A. pingue n. sp. 

 from the Four Mile Dam Formation in its normally lesser thickness, 

 lower convexity, emarginate or flattened anterior, and subtrigonal 

 rather than subpentagonal outline. It also is similar to A. succiduum 

 n. sp. from the Potter Farm Formation, differing in its larger size, 

 more numerous costae on the fold and flanks, sharper beak ridges, and 

 proportionately shorter median septa. 



Atribonium simatum is wider and less convex than A. halli (Fager- 

 strom) and A. rhomboidale (of Fagerstrom) ; its fold is lower, and 

 costae more numerous and weaker, and its anterior is flattened. It is 

 narrower and more weakly costate than A. savagei (Cooper) from 

 the Grand Tower Limestone of Illinois, its anterior margin is flatter 

 (or emarginate) and the shell outline subtrigonal, the profile lower 

 and less convex. A. simatum differs from A. Illinois ensis (Cooper), 

 also from the Grand Tower Limestone, in its flatter anterior, subtrig- 

 onal outline, lower fold, and more numerous costae on fold and flanks. 



Species of Atribonium that least resemble A. simatum are A. gregeri 

 (Branson), A. kernahani ( Whiteaves) and A. pauperum (Belanski). 

 A. simatum is not bulbous like A. gregeri, and it lacks the exaggerated 

 costae of the other two species. 



Occurrence and abundance. — Newton Creek Limestone, quarry of 



