LOGAN: CRETACEOUS INVERTEBRATES OF KANSAS. gi 



the descriptions correspond to tlie Niobrara form. For that reason 

 I have figured the Niobrara form and presented two views of the 

 upper valve and one of the lower one. A comparison between this 

 figure and Conrad's type should be made. 



Ostrea exog"yroidea, n. sp. Plate XX, Fig. 3. 



Shell small, thick, elongate, narrow, deep; beak long, curved 

 ventrally, lower valve very capacious, attached by entire lower sur- 

 face; posterior border short, only slightly rounded; dorsal border 

 possessing a concave curve near the middle portion; ventral border 

 possessing a corresponding convex curve; external surface marked 

 by concentric lines of growth which are not prominent; interior of 

 shell smooth, muscular striae on rim in anterior region; beak pos- 

 sessing an irregular area which is marked by ridges running parallel 

 to the longitudinal axis of the shell. 



Measurements: 



Length 30 mm 



Width 15 " 



Height 10 " 



Locality: White Rock creek north of Mankato, Jewell county, 

 Kansas. 



Geological horizon: Rudistes beds, Niobrara Cretaceous. 



Remarks. — This form is found associated with O. congesta and may be a variety 

 of that species. As will be seen by the description and figures it has marked dif- 

 ferences, however. The most noticeable one is that of the irregular, ribbed, 

 umbonal area which is concave beneath. I have collected only a few of the type; 

 further collections may reveal gradational forms. 



Modiola, sp.? Plate XX, Fig. 4. 



Shell medium size, convex, arcuate, elongately ovate; beak 

 terminal, slightly depressed; anterior end narrow; posterior end 

 dilated and sloping gradually to an almost yet never completely 

 level area at the posterior margin; postero-basal portion sloping 

 equally with posterior; antero-basal margin slightly reflex; basal 

 margin strongly yet uniformly curved; ventral side narrow, precip- 

 itous, with shallow depression running from beak to median por- 

 tion, slightly incurved at margin; ventral margin angular, with 

 apex of angle at median portion; hinge line straight, about half the 

 length of the ventral side; exterior of shell ornamented with more 

 or less prominent lines of growth which are crossed by uniformly 

 radiating ribs. The ribs are wavy and are more prominent in the 

 antero-basal region. They are also prominent in the basal region 

 and scarcely noticeable on the convex area of the valve. On the 

 ventral side they are well marked. 



