﻿4 TRUNCirXA 



IVIarsupial swelling- iiirtated, radially sculptured, extending to 

 the extreme posterior base. 

 Raised into a sharp ridge, ending in a sharp point behind, 

 shell triangular. T. triquetra. 



Not sharply elevated nor sharp behind. 



Much flattened below. T. arcceformis. 



Projecting below the base. T. penita. 



Marsupial swelling thin, compressed or subcompressed, round- 

 ed into a post-basal flap. 

 Swelling enormously produced, dark. T. perplexa. 



Swelling moderate in size. 



Usually dark. T. propinqua; capsceformis. 



Rarely dark. 



T. rangiana; bicmarginata; deviata ; sainpsonii. 



MALE SHELLS. 



Shell triangular. 



Without a radial depression. 



Much inflated ; posterior ridge high. T. triquetra. 



Moderately inflated ; posterior ridge not high. 



7\ compacta; modicella; penita; metastriata. 

 With a radial depression in front of the posterior ridge. 



T. sampsonii. 

 Very short. 



Chestnut-colored, glossy, radially sculptured behind. 



T. haysiana. 

 Yellow-green, rayed, not sculptured behind. 

 ' T. personata. 



Long triangular. T. propinqua. 



Shell subquadrate or subrhomboid. 

 Without a radial depression. 



Posterior ridge high, sharp. T. arcceformis. 



Posterior ridge rounded, sides flattened. T. brevidens. 

 With a radial depression. 



Depression wide, distinct, deep. T. foliata; lezvisii. 



Depression moderate, not deep. T. stcwardsoni. 



