176 AXNALS XEW YORE ACADEMY OF SCIEXCES 



vaiious lines, and to make a trial of the statistical method in the stndv 

 of fossLs. 



The curves were made hj plotting the percentages of the total nnmber 

 of indiyidnals having indices h-^T^^i- certain prescribed limits. The 

 indices were taken as absc-i?-- _ : ^ ereentages as ordinates. The 

 higher indices were indi? :t t :^ ~ md the lower on the left. 



Progr^sion has been indi:i:r _ _i - i _ :: — -ight to left. 



The mntation thedforden.se was t : : t ot Shimer and Graban in 

 1902.- Descriptions of the other mutations are taken to a large extent 

 from Graban mannscript. 



MrTATiox I. — Spirifer mucronatus mut. alpenetise Gbabau iis. 



This mtitation oc-curs in the lowest beds of the Michir 7:1 in 

 a shalv matrix. It is of moderate size, with fairlT stroi-^ ^: --wi:^ lines. 

 The plications are close together and are not very strong. They ni ::r '►e- 

 about fifteen on each side of the fold and sinus. The shell is som- _ _— 

 extended into a pair of mucronate wings. The sinus is broad and shallow 

 and conraizii :: median plication. The fold is also broad and shallow, 

 and son.-:- contains a median groove in the young stages. T'iitTt is 

 r-^rr ■--. HtLiiu groove on the _ f the adult. Three hun t :: ' 



icTe:irr-T~ : :_^"^duals of this iiL-.:a::on were znetiSTuned and the i:-^-:-^- 

 mg is a : _ of the results. The conip.r:e ziirasurements are given 



in the tables. 



Maxmiiim width rt2inm- 



MJTilTnuTn width 15 



Maxiinum lengtti 28 



MiulTTiTiTn lengOL 9 



Maximum shell index (adult) . 2.80 



Mmimum shell index (adult) 95 



Average shell index (adult) (about) . . 1.50 



Maximum shell index (neanic stage) 4.30 



MinlmTiTn shell index (neanic stage) 1 . 29 



Average shell index •' neanic stage> • about) . . 2.00 



Table I. — v :«*'r:'t"- of individuaJs and percentages of total numher of 

 indi rid u<j1js of variotts indices 



Index 



-1.00 



1.01-1.25 



1.26-1.50 Ill 



1.51-1.75 



1.76-2.00 





Adnlt 



A 





X 



eanjc 



f 

 Xuabe 



r Perc^'Ti^r 



X^-c^: 



r 



Pereentase 



3 



X 













63 



16-9 













111 



29. S 



1 





.2 



107 



^■i ~ 



15 





4.0 



1-- 



15.3 



51 





13.6 



-Ball GeoL So^ Am., vol. 13. pp. 149-ls6. 



