THE NAUTILUS. 79 



j2 J Posterior ridge rounded 13. 



(Posterior ridge more or less distinctly biangulate . . . .19. 

 , (Posterior slope distinctly flattened 14. 



(Posterior slope not flattened 18. 



, . (Umbonal region flattened 15. 



(Umbonal region inflated 16. 



( Shell subquadrate, subcompressed brevidens. 



15. -I Shell smaller, oval, less compressed, beaks more anterior. 

 (^ metastriata. 



f Shell distinctly triangular, anterior margin not projecting 

 ,' much beyond the anterior umbonal slope, unicolored or 



, ,, ] with capillary green rays 17. 



j Shell triangularly ovate, anterior margin projecting beyond 



the umbonal slope, conspicuously painted with green rays 



[ and blotches triquetra. 



( Beaks flattened, subcentral penita. 



\ Beaks higher, more anterior, shell smaller .... compacta. 



18 ("Shell small, subtriangular, thick and solid .... modicella. 

 (Shell larger, oval and thin lenior. 



Shell large, greatly inflated, thick, solid, posterior ridge very 

 prominent, posterior slope with a well-defined furrow, sur- 

 19. < face rough, rays capillary arcceformis. 



Shell smaller, less inflated, posterior ridge less developed, 

 surface smooth, broadly rayed with green 20. 



Q ( Shell subcompressed, elliptical capsczformis. 



(Shell smaller, short oval, quite inflated florentina. 



B. Females. 



, (Marsupial expansion swollen 2. 



(Marsupial expansion flattened 13. 



f Marsupial expansion an inflation of the posterior ridge . . 3. 



2. < Marsupial expansion in front of and distinctly separated 



( from the posterior ridge 9. 



f Posterior ridge angularly inflated and curved backwards . 4. 

 ( Posterior ridge roundly inflated and curved forwards . . 5. 



[ Posterior ridge sharp, dorsal slope obliquely truncate, flat- 



. tened, base of expansion rounded triquetra. 



j Posterior ridge less angular, dorsal slope not flattened, l>i- 

 [ angular, base of expansion flattened arcceformis. 



f Base of expansion distinctly projecting beyond the basal 



5 I line 6. 



j Base of expansion scarcely projecting beyond the basal 

 [ line 8. 



