CORRELATION OF GROWTH-STAGES AS EVINCED BY VARIOUS DIFFERENTIALS 



OF THE SHELL. 



■ tages. 



Form. 



Umbilication. 



Ornamentation. 



Septation 



(mbryonic 



Pbotoconch. 



' Ananepionic 



Conch broad, progress- 

 ively tapering in section. 



(a) 



epionic i JVletanepionic Conch section contracted. Abruptly increased. 



Paranepionic 



f Ananeanic 



anic \ Metaneanic 



phebic 



Paraneanic 

 Auephebic 



Metephebic 



Parephebic 



Conch section expanding. Again decreased but not 

 terminating in a ridge to (a). 

 or varix. 



First septum straight, 

 with distinct ventral 

 lobe- 



Smooth in all substages. 



with terminal varix i Second septum with 

 I inception of lateral 

 | saddle, progressively in- 

 I creased to end of stage. 



Gradual progress in con- Constant decrease of um 

 tour from a broad 

 subcrescentic section to 



an obcordate section. bilication by increasing 



degree of embracement 

 of successive whorls. 

 This decrease is a con- 

 In late ephebic conditions s t a n 1 1 y diminishing 



with increasingly less q" autit >'- 



Change from loss to gain 



convex lateral slopes, and 

 broader, more conspicu- 



ous ventral ridge. 



in umbilication which 



is maintained through 



Very strong, simple Continuation of develop- 

 varices crossing whorl 

 without curve. 



Varices in double or com- 

 pound series, a primary 

 and one or more second- 

 ary, crossing the whorl 

 without curve. 



ment, increasing size of 

 lateral saddles but with- 



XT . ii ii oat introduction of new 



\ ances much reduced and 



all of same size with 



broad hvponomic curve. , , , ,<, 



* 1 Jobes or saddles. 



Increasing incurvature introduction of ventral 



1 lobe,ventn>lateral saddle, 

 dorsal saddle, subdorsa- 

 ls L . lateral lobe, 

 of hvponomic sinus.] 



*** 



j Progressive increase* in 



, r . j , . ,. I lobes and saddles, con- 

 V ances reduced to lines ,. , , ■, , ' £ 



tinned bluntness of 



lateral lobe. M. si?nu- 



Anagerontie The sides of the wnori dis- 

 tinctly concave and ven later ephebic and prob- 



Ar . .. | tral ridge pronounced; 



krontie > Metagerontic . . " . r . i 

 I ; e I cannate in tacnygenic 



species, M. o.ry, .1/. 



Paragerontic vagans. i ably gerontic stages. 



showing a tendency to 

 gather in fasicles which 

 may take the form of 

 low pilae. 



lator stage. 



Normal adult characters 

 with acuteness of lateral 

 lobes. 



Lateral enlargement of 

 lateral saddle producing 

 a shouldered appearance. 

 Septa parallel and 

 crowded in tachygenic 

 forms : M. accelerans. 



