60 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



Occurrence and abundance. — "Upper part of Alpena Limestone" 

 (now Four Mile Dam) at Four Mile Dam in Thunder Bay River, sec. 

 7, T-31-N, R-8-E, Alpena County, Mich. (44 specimens USNM 

 141920-22) ; upper part of Alpena at Four Mile Dam (3 specimens 

 USNM 141929) ; Four Mile Dam Formation, at Four Mile Dam, S. 

 y 2 , sec. 7, T-31-N, R-8-E, 3 miles NW. of Alpena, Mich. (2 speci- 

 mens USNM 141923) ; upper blue shale of Gravel Point Formation of 

 Cooper and Warthin (1942) in Bell Quarry, NW. y A NW. ]/ A , sec. 9, 

 T-34-N, R-6-W, 2.3 miles E. of Bay Shore, Mich. (16 specimens 

 USNM 141924-6) ; just under upper blue shale of Gravel Point For- 

 mation, on shore of Lake Michigan opposite Pennsylvania Railroad 

 station, Bay View, Mich. (6 specimens : aff. A. pingue USNM 141927, 

 141930) ; upper blue shale of Gravel Point Formation, Quarry of 

 Charlevoix Rock Products Co., SE. y A , sec. 28, T-34-N, R-8-W, 

 Charlevoix County, Mich. (2 specimens: aff. A. pingue USNM 

 142928). 



Age. — Middle Devonian. 



ATRIBONIUM ROSTRATUM Grant n. sp. 



Plate 3, figs. 2-2a 



Shell small, wedge-shaped, greatest width and thickness located 

 near anterior ; commissure uniplicate ; fold broad, flat, beginning about 

 5 mm. anterior to brachial beak, producing definite flat elevation of 

 brachial valve; sulcus shallow, greatest depression located near ante- 

 rior geniculation of shell ; costae low, rounded to bluntly pointed, 

 beginnings 3-5 mm. anterior to beaks, numbering three to six, nor- 

 mally four on fold, one fewer in sulcus, two or three weaker ones on 

 each flank ; anterior margin flattened, slightly convex outward ; growth 

 lines fine, most obvious on flattened anterior region ; growth laminae 

 slightly stronger, widely and irregularly spaced. 



Pedicle valve flatly convex, with slight swelling anterior to beak, 

 strong geniculation near anterior margin, bending abruptly toward 

 commissure; beak long, suberect, apex sharp, standing well away 

 from brachial beak, providing ample space for delthyrium and small, 

 conjunct deltidial plates ; foramen narrow, cutting apex of beak ; beak 

 ridges sharp, proportionately long. 



Brachial valve more strongly convex transversely, flatly convex 

 but rather steeply sloping upward toward anterior, there abruptly 

 geniculated toward commissure ; beak extending into pedicle valve, 

 apex hidden beneath deltidial plates. 



Pedicle valve interior with spondylium sessile for about 1 mm. in 

 apex of beak, elevated on median septum farther anterior ; septum 

 extending forward about half length of valve. 



