[ANNAiS N. y. Acad. Sci., Vol. XXVI, pp. 175-214. 30 June, 1915] 



STATISTICAL STUDY OF VARIATION m SPIEIFER 



MUCEO^^ATUS 1 



By Charles C. Mook 



(Presented in ahsfracf hefore tlte Acadeniij, 7 Deceiuher, 1014) 



CONTENTS 



* I'age 



Introduction 175 



Mutation I. — Spirifer mucronatus mut. alpenense Grabau ms 176 



Mutation II. — Spirifer mucronatus mut. multipUcatus Grabau ms 177 



Mutation III. — Spirifer mucronatus mut. profundus Grabau ms 179 



Mutation IV.- — Spirifer mucronatus mut. thedfordense Shimer and Grabau. 182 



Mutation V. — Spirifer mucronatus mut. attenuatus Grabau ms 184 



Conclusion 186 



Tables of measurements and indices 190 



Inteoduction" 



These studies were made on specimens of five mutations of Spirifer 

 inucronatus collected b}' Professor A. W. Grabau and Dr. H. W. Shimer 

 near Thedford, Ontario, and by Professor Grabau near Alpena and at 

 other localities in Michigan. 



The beds from which these fossils were collected correspond, in whole 

 or in part, with the Hamilton of jSTew York State. The general suc- 

 cession of beds in the Michigan region is given below. At the base are 

 calcareous shales corresponding in a general way with the lower part of 

 the Hamilton or upper part of the Marcellus of the ISTew York State 

 section. These shales contain the mutation of Spirifer mucronatus called 

 by Grabau alpenense. Above these shales there is a series of alternating 

 limestones and calcareous shales. The limestones contain the mutation 

 multiplicatns and the shales contain the mutation alpenense. Above this 

 series there is another series of calcareous shales containing the mutations 

 profundus and attenuatus. In the Thedford section, the mutation thed- 

 fordense Shimer and Grabau occurs in shales corresponding approximately 

 with those containing profundus and attenuatus in Michigan. 



The objects of the studies were to determine, if possible, the relations 

 of the different mutations to each other, the progress of evolution in the 



^ Manuscript received by the Editor IG December, 1914. 





