Weller — Kinderhook Faitnal Studies. 189 



tened toward the cardinal extremities ; the mesial fold scarcely 

 elevated above the general surface of the valve, marked by 

 dichotomizing plications which are from four to six in number 

 at the front margin. Surface of each valve marked by from 

 fifteen to twenty-five plications on each side of the fold and 

 sinus, all of which are often simple but with the first one or 

 two adjacent to the fold and sinus sometimes divided. Entire 

 surface also covered by concentric lines of growth which are 

 lamellose on perfectly preserved shells. 



Remarks. The most typical form of this somewhat vari- 

 able species is that which occurs in the Louisiana limestone 

 of Pike and Marion counties, Missouri. The specimens from 

 the oolitic limestone at Burlington are usually somewhat 

 smaller than the largest individuals from the Louisiana lime- 

 stone, and the beak of the pedicle valve is less incurved. 

 In all other respects, however, examples from the two locali- 

 ties are identical, and it seems impossible to consider them in 

 any other light than as members of a single species. 



DlELASMA ALLEI (Win.). 



For a full description with illustrations of this shell, the 

 reader is referred to page 162 of the present paper. The 

 types of the species are from both the upper yellow sandstone 

 and the oolite bed at Burlington. The single specimen from 

 the oolite bed is but a fragment of one valve, but it is prob- 

 ably the same species as the more perfect specimen from the 

 yellow sandstone below. The description of the shell struct- 

 ure given by Winchell, was drawn wholly from this oolite 

 specimen. 



MOULUSCA. 



PELECYPODA. 



Pernopecten cooperensis (Shumard). 



Pi. XVII. f. 1 . 



This species has already been fully described and discussed 

 in these studies.* The specimens in the oolite bed are typical 

 of the species described by Hall from this same locality as 



* Trans. Acad. Sci. St. Louis. 9 : 24. 



