ADDEND'A. 417 



Spiiifera whitaeyi. 



Spirifera whitneyi: Hall. Geological Report of Iowa, p. 502, plate 4, f. 2. 1859. 



This species is referred to on page 245, as derived from beds of the age 

 of the Hamilton group, in Iowa. More recent observations, with pretty 

 extensive collections made in several localities in Iowa, by Mr. R. P. Whit- 

 field in 1866, have led to the conclusion that this species, together with its 

 associates in the same locality, are of higher beds than those of the Hamil- 

 ton group and should properly be referred to the age of the Chemung. 



Some further notice of the species thus associated, will appear in the 

 State Cabinet Report. 



Spirifera mesastrialis. 



PLATE LIT, FIGS. 14-22, 



This species, in its varieties of form, has heretofore been referred to the 

 Chemung group only. More recent collections, with better knowledge 

 of the limits of the Chemung and Hamilton groups in the eastern part 

 of the State, have shown its occiu-rence in the two formations. The speci- 

 mens from Schotarie county are from rocks of the Hamilton group, and are 

 separated from those in Delaware county by almost non-fossiliferous beds of 

 several hundred feet in thickness. It is a little remarkable that while the 

 geographical range of the species is less than two hundred miles, its vertical 

 range should be so very great. 



RliyDcIionella (Stenocisma) contracta var. saxatilis. 



PLATE LIV A, FIGS. 44-51. 



Among the collections from Rockford, Iowa, there are some specimens of 

 Rhynchonella, which possess many of the characteristic features of R. con- 

 tracta of the New York Chemung group, and also those of R. eximia 

 of the same formation. The examples figured on plate 54 A, figs. 44-49, 

 have much the appearance of the former species, except in size, while the 

 [Paleontology IV.] 54 



