PELECYPODA—PRIONODESMACEA. 



459 



c. Lower valve attached by whole lower surface and deep 22. 



22. Sides bent up from area of attachment almost at a right angle. 



266. O. congesta. 

 22. Sides curved upward 259. O. strigilecula. 



c. Lower valve not attached by whole lower surface 33. 



33. Shell winged posteriorly 275. O. bryani. 



33. Shell not winged posteriorly aa. 



aa. Lower valve broadest below middle f. 



f. Lower valve very convex in central portion. 



270. O. subspatulata. 

 f. Lower valve very convex towards umbo. 



280. O. vomer. 



aa. Lower valve broadest at middle ff. 



ff. Large 282. O. compressirostra. 



|f. Small 268. O. cretacea. 



Both valves only slightly convex d. 



d. Outline subtriangular 44. 



44. Large, 3-4 inches high 283. O. trig ona lis. 



44. Small, not 2 inches high 274. O. plumosa. 



d. Outline elongate-oval 55. 



55. Shell attached by whole under side 278. O. inornata. 



55. Shell not attached by whole under side bb. 



bb. Shell slightly arcuate laterally ttt- 



Iff. Large (3 inches X l }4. inches) 276. O. glabra. 



flf. Small (2 inches X J inch) 277. O. subirigonalis. 



bb. Shell not arcuate laterally 4f. 



4f. Margins crenulate 269. O. denticulifera. 



4f. Margins not crenulate 264. O. haydeni. 



d. Outline round-oval 284. O. percrassa. 



d. Outline very long and narrow with nearly parallel sides. 



263. O. soleniscus. 



259. 0. strigilecula White. (Fig. 609.) 



Jurassic. 



Fig. 609. Ostrea strigilecula. ( Kan. Univ. Quarterly. ) 



Small (up to 1 inch in diameter). Lower valve attached by 

 entire surface. 



Throughout the Jurassic of the Interior. 

 260. 0. crenulimargo Roemer. (Fig. 610.) Comanchic. 



Thin, subtriangular. Beaks short and blunt. Lower valve 



