NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA GRANT 45 



Michigan Alkali Co., Alpena, Mich. (151 specimens USNM 141974- 

 5, 141980-82) ; Dock Street Clay of Grabau (1902) of Alpena Lime- 

 stone, Thunder Bay Quarry, Alpena, Mich. (1 specimen USNM 

 141984) ; Newton Creek east side of French Road, ^ mile south of 

 NW. corner, sec. 16, T-32-N, R-8-E, Alpena County, Mich. (1 speci- 

 men USNM 141979: float); Alpena Limestone, 0.15 mi. south of 

 NW. corner, sec. 11, T-31-N, R-8-E, on Long Lake Road, Alpena 

 County, Mich. (1 specimen USNM 141983) ; lower 10 feet of Ferron 

 Point Formation, at Rockport Quarry, Rockport, Mich. (1 specimen 

 USNM 141978). 



Age. — Middle Devonian. 



ATRIBONIUM COOPERORUM Grant n. sp. 



Plate 2, figs. 3-3c ; figure 7 



Shell small, flatly biconvex; outlines subtrigonal to subpentagonal, 

 length and width nearly equal, greatest width near midlength; com- 

 missure uniplicate ; fold high, rather broad, with gently arched or flat- 

 tened crest, forming prominent fold on brachial valve beginning 4-8 

 mm. anterior to beak ; sulcus extended as tongue at anterior to fill arch 

 of fold, producing broad shallow trough in pedicle valve beginning 4-8 

 mm. anterior to beak, costae moderately strong, with bluntly angular 

 crests, beginning 4-6 mm. anterior to beaks, numbering four to six on 

 fold (normally four), one fewer in sulcus, four to six on each flank 

 (normally six) ; anterior margin gently rounded or slightly flattened, 

 not emarginate, valves meeting at less than straight angle at anterior 

 commissure ; growth lines fine, closely spaced ; growth laminae weak, 

 irregularly spaced, rarely observed. 



Pedicle valve flatly convex, with greatest convexity just anterior 

 to beak, abruptly flexed toward commissure at anterior flanks, more 

 evenly and gently curved along midline through sulcus; beak sharp, 

 strongly curved, suberect to erect ; beak ridges short, sharp ; postero- 

 lateral slopes slightly concave in outline but not flattened ; delthyrium 

 small, constricted by pair of small, acutely triangular, conjunct or dis- 

 junct deltidial plates, leaving small slotlike foramen penetrating apex 

 of beak in some specimens. 



Brachial valve more strongly convex transversely, less convex lon- 

 gitudinally, slightly swollen near back, fold prominent at anterior, 

 abruptly bent toward commissure at anterior flanks, more gently bent 

 at anterior of fold ; beak short, rounded, apex within delthyrium, ob- 

 scured by deltidial plates. 



Fig. 6. — Scatter diagrams of dimensions of Atriboniutn simatum from Alpena, 

 Mich. 



