228 



NORTH AMERICAN INDEX FOSSILS. 



XXXVIII. Schuchertella Girty. 

 (Orthothetes of authors.) 

 Shell flat. Much like Strophomena. Pedicle valve with well- 

 developed, cardinal area, often irregular. Brachial valve with nar- 

 row cardinal area. Cardinal process bilobed when viewed from 

 within, quadrilobed when viewed from without ; a faint median 



Fie 



Schuchertella subplana. (After Hall.) 



septum present. Surface covered with slender radiating striae crenu- 

 lated by sharp concentric growth lines or fine plications. Sil.-Carb. 



105. S. subplana (Conrad). (Fig. 276.) Siluric and Devonic. 



Length and width nearly equal. Hinge line extended. Pedicle 

 valve at first convex, later becoming concave. Striae coarse, sharp 

 and angular. 



Niagaran and Helderbergian of New York, Kentucky, Tennessee, 

 Indiana, Illinois, Missouri, Ontario, Nova Scotia, Anticosti. 



106. S. interstriata (Hall). 

 (Fig. 277.) Siluric. 



Semioval, subplano - convex. 

 Pedicle valve much elevated at 

 the beak. Radiating striae strong, 

 not arcuate, with interstitial striae 

 beginning below the beak. In- 

 terior of shell marked with di- 



chotomous, radiating striae. All radiating striae crossed by rather 



strong growth lines. 



Fig. 277. Schuchertella interstriata. 



