LOGAN: CRETACEOUS INVERTEBRATES OF KANSAS. OQ 



Remarks. — This species is found associated with O. canonensis. Its determina- 

 tion is based upon a number of forms which differ somewhat in general outline, 

 but in other characteristics do not vary to any marked extent. 



Ostrea "wellerii, n. sp. Plate XX, Figs. 6, 7. 



Shell (right valve) long, narrow, nearly flat, irregular in general 

 outline; borders somewhat wavy; test thin, greatest thickness near 

 beak; beak incurved; exterior surface irregularly curved, smooth, 

 umbonal region possessing a horse-shoe shaped depression; general 

 curve of dorsal margin convex but irregularly so; ventral border 

 concave; anterior border rounded; posterior border obtusely tri- 

 angulate; interior of shell marked by branching depressions; shell 

 considerably larger posteriorly, narrow between beak and central 

 region. Individuals not growing attached. 



Measurements: 



Length 65 mm 



Maximum with 30 " 



Height 3 - 



Locality: Ellsworth county, Kansas, near Kanapolis. 



Geological horizon: Lower Cretaceous. 



Remarks. — The individuals of this species are not essentially different in any 

 respect except in general outline. The difference in this particular is not as 

 strongly marked as in many other species. O. wellerii is found associated with O, 

 kansasensis and O. willistonii. 



Ostrea willistonii, n. sp. Plate XXI, Figs. 5, 6. 



Shell (left valve) orbicular, medium size, elevated, strongl}' con- 

 vex, margin radiately ribbed; ribs extending*utward into elongated 

 tips, five of which are very prominent; test thick, greatest thick- 

 ness in marginal region; beak obtusely pointed; dorsal border in 

 the form of an elliptical curve; ventral border slightly concave; 

 anterior border pointed; posterior border obtuse, rounded; interior 

 of valve marked by a deep fossa, having in its posterior part the 

 muscular impression; exterior surface marked by very prominent 

 lines of growth. 



Measurements: 



Length 40 mm 



Width , 35 '< 



Height 12 " 



Locality: Ellsworth county, Kansas, near Kanapolis. 



Geological horizon: Lower Cretaceous. 



Remarks — This species is based on a number of collected individuals, sorile of 

 which are less irregular in outline. None of these forms approach the two species 

 with which this one is associated. I do not believe that it can belong to the same 



