LOGAN: CRETACEOUS INVERTEBRATES OF KANSAS. 95 



Lower valve thin, flat, thickness greatest at the beak; underside 

 of beak showing flat, smooth surface of attachment. 



Both valves are marked by a deep notch in the antero-dorsal 

 region. 



Measurements: 



Length 46 mm 



Width 25 " 



Height 08 " 



Locality: Saline river, Ellis county, Kansas. 



Geological horizon: Rudistes beds, Niobrara Cretaceous. 



Remarks. — Figures 7 and 10 represent views of an adult, while 8 and g are 

 young individuals. The groove on 9 is probably due to pressure. 



Ostrea je-wellensis, n. sp. Plate XXII, Fig. 11. 



Shell (right valve) thin, medium size, ovate, convex; greatest 

 convexity a little more than one-third the distance back from the 

 beak, shell surface sloping gradually from this point to the poster- 

 ior border and more abruptly toward the beak; sloping still more 

 abruptly to each side and ending in wing-like areas, which are 

 almost flat but are crossed by oblique ridges and depressions. The 

 beak is straight, ending in a triangular form with a smooth area on 

 the under side. The borders on each side of the beak are turned 

 inward a little and crossed by transverse ridges. The exterior sur- 

 face of the shell is smooth, not showing lines of growth but more 

 or less prominent ridges on marginal areas; posterior border round- 

 ed in convex curve; dorsal and ventral borders alike forming con- 

 vex curves with depressions near the beak. 



Measurements: 



Length 35 mm 



Width 15 " 



Height : 8 " 



Locality: White Rock creek, Jewell county, Kansas. 



Geological horizon: Rudistes beds, Niobrara Cretaceous. 



Remarks. — This form may be a variety of O. inciirva. However, among a 

 number of specimens examined there appeared no gradational forms. 



FAMILY OSTREID/E. 



Pseudo-perna, nov. gen. 



Shell varying in size, shape, and thickness; beak of lower valve 

 split transversely into two equal parts; hinge line of right valve 

 possessing at a short distance from the beak a projection, between 

 which and the beak the border is crossed by short rounded trans- 

 verse ridges; surfaces vary from smooth to deeply iriibricated; mar- 

 gins in some species reflex and crenulate. 



