THE NAUTILUS. 79 



12. J Posterior ridge rounded 13 



(Posterior ridge more or le.«s distinctly bianguiate . . . , 19. 



13. I Pos^^'"'0'" slope distinctly flattened I4 



( Posterior slope not flattened ... IS 



14. f Umbonal region flattened j5 



(Umbonal region inflated ' 16 



r Shell subquadrate, subcompressed brevidens 



15. -j Shell smaller, oval, less compressed, beaks more anierior." 

 p- metastriatu. 

 [Shell distinctly triangular, anterior margin not projecting 



much beyond the anterior umbonal slope, unicolored oT 



16. { , ^"'1 capillary green rays I7 



I Shell triangularly ovate, anterior margin 'projecting beyond 

 , the umbonal slope, conspicuously painted with green rays 

 i «"^1 l^lotches triquetra 



17. .fg^^aks flattened, subcentral Va. 



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



18. |g['«^|Jfniall,subtriangular, thick and solid .. . . modicella. 



(bhell larger, oval and thin lenior. 



f Shell hirge, greatly inflated, thick, solid, posterior ridge very 



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



i /ace rough, rays capillary arc^formis 



\ Shell smaller, less inflated, posterior ridge less developed 



[ surface smooth, broadly rayed with green 20. 



20. I Shell subcompressed, elliptical capscBformls. 



(J5hell smaller, short oval, quite inflated ^«^o.,*.-..„ 



quite inflated florentb 



B. Females. 



(Marsupial expansion swollen 2 



(Marsupial expansion flattened , 13' 



r Marsupial expansion an inflation of the posterior rid're 3 

 -j Marsupial expansion in front of and distinctly s"eparated 

 ( 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 



Posterior ridge less angular, dorsal slope no't flattened, bi- 

 angular, base of expansion flattened arcceformis. 



fBase of expansion distinctly projecting beyond the basal 

 I line ^ 



j Base of expansion scarcely projecting' bey'ond the basai 

 L line "^ Q 



