NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA GRANT 6l 



Brachial valve interior with camarophorium beginning against shell 

 floor, separated from hinge plate by intercamarophorial plate ; median 

 septum extending anteriorly beyond midlength of valve. 



Holotype.— USNM 141950, plate 3, fig. 2a. 



Table 8. — Measurements of Atribonium rostratum from the Thunder Bay Lime- 

 stone at Partridge Point, Mich. 



Measurements, in millimeters 



Comparisons. — Atribonium rostratum is characterized by its small 

 size, long pedicle beak with perforated apex, subtrigonal outline and 

 profile, and its few lateral costae. The beak is similar to that of A. suc- 

 ciduum n. sp. from the Potter Farm Formation, but A. rostratum has 

 sharper costae and a convex rather than slightly concave anterior mar- 

 gin. It is smaller than A. simatum n. sp. from the Alpena Limestone, is 

 not as thick, has fewer costae on fold and flanks, and has a proportion- 

 ately shorter beak. It is larger and not as thick at the anterior as A. 

 kernahani (Whiteaves) ; smaller and not as globose as A. gregeri 

 (Branson) ; thicker and more costae than A. halli (Fagerstrom). It is 

 smaller, narrower, and has fewer costae than A. savagei (Cooper) or 

 A. illinoisensis (Cooper) from the Grand Tower Limestone of Illinois. 



Occurrence and abundance. — Thunder Bay Limestone, on Partridge 

 Point, south of Alpena, Mich. (44 specimens USNM 141951) ; Thun- 

 der Bay Limestone, on Partridge Point, south of Alpena, Mich. (8 

 specimens USNM 141954) ; Thunder Bay Limestone at Partridge 

 Point, Mich. (6 specimens USNM 141953). 



Age. — Late Middle Devonian. 



