Logan: cretaceCus invertebrates of Kansas. 97 



Length 38 mm 



Width 30 " 



Height 6 " 



Locality: Solomon river near Marvin, Pliillips county, Kansas, 

 and Smoky Hill river, Trego county, Kansas. 



Geological horizon: Rudistes and Hesperornis beds, Niobrara 

 Cretaceous. 



Remarks. — All the species of this genus have the coloring matter of the periphery 

 of the shell well preserved. So well, indeed, that they have the appearance of 

 shells just taken from the ocean. This fact leads to the following conclusions: 

 First, that the shells were imbedded in their matrix of chalk before they had 

 weathered even to a slight degree; second, that the chalk acts as a preservative 

 agent for the coloring matter; and that the chalk forms must have been deposited 

 at a very rapid rate in order to have produced the first result. 



Pseudo-perna attenuata, n. sp. Plate XXIII, Figs. 8, 9. 



Shell (right valve), tliin, oblong, convex, convexit}' greatest 

 along median line, beak sharp pointed; turned toward ventral bor- 

 der; hinge line long, possessing near the beak a very prominent 

 projection; area between the beak and projection occupied by sev- 

 eral transverse ridges, remainder of ventral border straight; exterior 

 surface smooth except near the margins where it is marked by con- 

 centric lines of growth. 



The posterior border is truncate; dorsal border broadly curved, 

 anterior border short, rounded. The interior of the shell is smooth. 

 The muscular impression is small. 



Measurements: 



Length 41 mm 



Width 27 " 



Height 7 " 



Locality: Solomon river, Phillips count}', Kansas. 



Geological horizon: Rudistes beds, Niobrara Cretaceous. 



Remarks. — The ventral border projection is more prominent in this species than 

 in any other of the genus. The general shape of the shell corresponds more near- 

 ly to P. riigosa but the test has not half the thickness. 



Pseudo-perna orbicularis, n. sp. Plate XXIII, Figs. 10, 11. 



Shell (left valve), large, orbicular, convex, beak split horizontall}' 

 into two equal parts, turned slightly toward ventral border; ex- 

 terior surface of shell smooth except in the posterior region where 

 it is marked by concentric lines of growth; ventral border irregular, 

 crenulate and slightly reflex; posterior border nearl}^ straight; dor 

 sal border moderately convex; anterior border pointed; test ot 



