Apr. 1899. Paleontology of Upper Cretaceous Series — Logan. 213 



ond lateral sinus nearly resembling one of the divisions of the first, 

 and in the adult with merely a number of marginal digitations; sec- 

 ond lateral lobe little more than one-third as long, and from one- 

 third to one-half as wide as the first, generally tripartite at the end, 

 but sometimes in large specimens, bipartite on one side of the shell, 

 the divisions being very simple and short, or serrated; third lateral 

 sinus very small and merely bilobate, or in large specimens digi- 

 tate along the margins; third lateral lobe hardly half as long as 

 the second, and in small specimens merely tridentate at the 

 end." 



The suture, shown in Fig. 2, PI. XXIV, is from a specimen evi- 

 dently much larger than any seen by Meek. The diameter of the sep- 

 tate portion is more than two inches and although the non-septate 

 part is not known it is probably at least three inches in diameter. 

 The specimens here figured were collected from the Blue Hill shales 

 of the Benton, in Osborne County, Kansas. 



THE GENUS OSTREA. 



The genus Ostrea has many representatives in the strata of the 

 Cretaceous System, although the entire system comprises a part only 

 of its geological range. Its distribution was as wide as the distribu- 

 tion of the genus to-day plus its distribution in the epicontinental 

 seas. A few species are common to Asia, Europe, Africa and North 

 America. Five species are common to Africa, Europe and North 

 America. Fifteen species found in Africa are also found in Europe. 

 One species not found in Europe is common to Africa and North 

 America. The Lower Cretaceous seas furnished the greatest abund- 

 ance of species and individuals. 



During middle Upper Cretaceous times the waters of the Ameri- 

 can epicontinental seas were too clear or lacked some characteristic 

 conducive to the life of Ostreae, for few species or individuals are 

 present in the strata except a very small form which was probably 

 able to adjust itself to the environments. This species, Ostrea con- 

 gesta, is one of the best known and most widely distributed of the 

 genus. It is remarkable also for its abundance. 



Probably the greatest beds of fossil Ostrea in existence are in 

 the Lower Cretaceous strata of Texas. .There beds of almost pure 



