1 82 NORTH AMERICAN INDEX FOSSILS. 



8* Beak of pedicle valve much less prominent... g // . 

 g // Shell usually piano convex (pedicle valve 



convex) LXXXVII. Centronella. 



g ,f Shell biconvex ; length but slightly greater 



than breadth XC. Crancena. 



8f Length greater than breadth, brachidium a spiral. 



CXV. Whitfieldella. 

 mm. Beak of pedicle valve not truncated by a round foramen ; 



brachidium a spiralium or complex loop g-f. 



9f Median sinus a mere groove CXVII. Nucleospira. 



9f Median sinus very broad and ill-defined ; no fold 

 . f CXX.* Meristina. 



preSent \ CXXIV.* Meristella. 



9f Median sinus very broad and pronounced, sides angu- 

 lated, fold pronounced and with median groove. 



CXXV. Pentagonia. 

 9f Median sinus and fold both present and of normal 



width 9* 



9* Sinus and fold only upon the anterior portion of the 



shell, spire very short XCVIII. Cyclospira. 



9* Sinus and fold extending from umbo \o" 



io // A broad plication present on each side of 

 median sinus and fold... CXVI Hyatella. 



lo // No plications present CV. Martinia. 



333. Median sinus and fold absent mm. 



nn. Beak of pedicle valve truncated by a round foramen... iof. 

 I Of Length and breadth subequal ; brachidium a spire.. IO*. 



10* Concentric growth lines lamellose n". 



ii //r Edges of the lamellae spinose. 



CXX II. CleiothyHs. 

 II 77 Edges of the lamellae not spinose. 



CXXI. Athyris. 

 IO* Concentric growth lines few and not lamellose. 



CXV. Whitfieldella. 

 iof Length greater than breadth or subequal ; brachidium 



a loop II* 



II* Umbo comparatively narrow ; shell elongate.. 12". 

 12" Concentric growth lines usually well marked. 

 LXXXIX. Cryptonella. 

 I2 /7 Concentric growth lines usually not prom- 

 inent XCI. Eunella. 



II* Umbo broad; shell elongate.. XCII. Terebratula. 

 II* Umbo broad ; shell subcircular.. XCV. Kingena. 



nn. Beak of pedicle valve not truncated by a foramen u|. 



I if Prominent cardinal area present. 



380 . Reticula ria perplexa . 



Ilf No cardinal area present CXVII. Nucleospira. 



j. Shell radially plicate or striate; brachidium wanting in some forms... 444. 



* These two genera are separated by the character of the loop. 





