228 PROCEEDINGS OF THE ACADEMY OF [1888. 



with P. cora; the vertical range of which would extend downward 

 to the base of the subcarboniferous. 



Produotus muricatus Norwood and Pratten. 



Productus muricatus Norwood and Pratten, 1854. Jour. Acad, 

 Nat. Sci. Phila., Vol. Ill, p. 14, pi. i, fig. 8. 



Productus muricatus White, 1875. Exp. and Sur. w. 100 merid. 

 vol. IV, pt. I, p. 120, pi. viii, fig. 4. 



In the geology of Yorkshire, (p. 214, jil. viii, fig. 3) Phillips in 

 1836 described Producta muricata: but the description is very brief 

 and his figure would indicate that he had in hand a specimen of 

 less than average size of P. costatus described by Sowerby nine 

 years before. In Iowa, Dr. White found Norwood and Pratten's 

 P. muricatus, most characteristic of the middle coal measures ; the 

 recent discoveries, however, show that it is the most abundant 

 brachiopod of the lower coal measures in the region around Des 

 Moines, yet the average size is somewhat less than that of the 

 same species from the calcareous strata of the middle coal measures 

 of the same locality. Both Davidson and Meek regard P. muricatus 

 N. and P. identical with P. longispinus of Sowerby. Throughout 

 Iowa at least, P. imiricatus N. and P. presents characteristics that 

 are remarkably constant ; and when associated with P. longispinus 

 no hesitancy whatever would be entertained in separating the two 

 forms. The species of Prodi<cft(s described have been numerous, as 

 is attested by an extensive and remarkable synonymy, which is only 

 too apparent to those who have given the subject careful attention. 

 The wide geographical distribution of some sj)ecies, and the extensive 

 vertical range of others, together with the concomitant differences 

 of environment at the time when the species were living, readily 

 accounts for the extreme variations presented. Inattention to this 

 important factor has often led to the basis of species upon super- 

 ficial characters which are relatively unimportant as classificatory 

 criteria, and the confusion arising therefrom has rendered the study 

 of this group extremely unsatisfactory. 



Chonetes mesoloba Norwood and Pratten. 



Chonetes mesoloba Norw^ood and Pratten, 1854. Jour. Acad. 

 Nat. Sci. Phila., Vol. Ill, p. 27. 



Chonetes mesoloba White, 1875. Expl. and Surveys w. 100 me- 

 rid.. Vol. IV, p. 123, pi. ix, fig. 7a. 



This species is one of the most abundant of the brachiopods 

 occurring in the bituminous shales of this locality. The average 



