MOLLUSCA—PELECYPODA. 365 



i // . Shell higher posteriorly than anteriorly a" '. 



a // . Umbonal ridge obsolete II. Clinopistha. 



a // . Umbonal ridge present IX. Orthodesma. 



i". Shell width subequal posteriorly and anteriorly. 



XIII. Palczanatina . 



**. No sinus anterior to umbonal ridge 2" ' . 



2 ,f . Shell broadly oval b" '. 



b" '. Depression posterior to umbonal ridge. 



XII. Saffordia. 



b". No depression posterior to umbonal ridge i //f . 



/ /// . A narrow ridge present behind the beaks. 



XIX. Edmondia. 



/"'. Ridge absent XX. Fordilla. 



2 n '. Shell narrowly oval c // . 



c // . Umbonal ridge noticeable only above, near the 



hinge XL Glossites. 



c n '. Umbonal ridge as inconspicuous above as below. 



3'". 

 2 /N '. Posterior adductor scar three times size of 



anterior XVII. Psiloconcha. 



2 /n ' . Adductor scars subequal III. Phthonia. 



II. Shell very long and narrow bb. 



bb. Posterior umbonal slope with different sculpture from rest of shell. 



VI. Orthonota. 



bb. Posterior umbonal slope not differently sculptured ff. 



ff. Antero-basal end of shell notched V. Prothyris. 



|f. Antero-basal end without notch IV. Sanguinolites. 



a. Shell subcircular, with radial sculpture and prominent, incurved beaks. 



XVI. Cardiopsis. 

 Beaks subcentral b. 



b. Shell transversely elongate 22. 



22. Surface radially sculptured cc. 



cc. Umbonal slope conspicuous XIV. Tellinopsis. 



cc. Umbonal slope very inconspicuous I. Solemya. 



22. Surface without radial ribs or striae dd. 



dd. Shell abruptly attenuate posteriorly CXXX. Cuspidaria. 



dd. Shell not attenuate posteriorly Iff. 



fff. Beaks very strongly incurved X. Grammysia. 



fff. Beaks not prominently incurved ..***. 



***. Furrow extending from beak to posterior basal margin. 



VIII. Ilionia. 



***. Shell lacking posterior furrow XIX. Edmondia. 



b. Shell sub-circular or vertically elongate 33. 



23. Surface with radial sculpture strongest ee. 



ee. Surface with radiating ribs tttt- 



-j-ff-f-. Hinge line straight ****. 



****. Umbo high, narrow XXI. Panenka. 



****. Umbo low, broad XXIV. Bttchiola. 



■(■f-ff. Hinge line curved ; also ribs numerous, small. 



XXIII. Paracardium. 

 ee. Surface with fine radiating striae XXII. Ontario. 



