168 Trans. Acad. Sci. of St. Louis. 



terior side having no siuus. Beak of the right valve minute, 

 depressed, situated at two -fifths of the length of the hinge 

 from the anterior extremity." 



" Surface marked by from forty-five to fifty rugose, 

 radiaiing plications, which sometimes bifurcate ; those on the 

 body of the shell about twice as wide as the interspaces; 

 while those on the sides are much finer. The depression, 

 separating the anterior auricle on the right valve, has but one 

 plication. Strong, undulating concentric lines cross the radii, 

 giving them their rugose surface." 



The dimensions of the type specimen are, length 27 mm., 

 and height 17 mm. 



Remarks. It has already been shown * that the two type 

 specimens >>f White and Whitfield's Aviculopecten nodocosiatus 

 are really representatives of two distinct species, and one of 

 these species from the Chonopectus sandstone has been pro- 

 visionally referred to Pterinopecfen laetus Hall. The specimen 

 which is retained as the type of P. nodocostatus is from the 

 upper yellow sandstone and is the only example which has 

 been observed. The original description of the species was 

 based for the most part upon this specimen, and in the pre- 

 ceding copy of this description all references to the left valve, 

 which was the Chonopectus sandstone specimen, have been 

 omitted. 



Pernopecten coopkrensis (Shum.). 



PI. XV. f. 5-6. 



A description and discussion of this species has already 

 been published in Kinderhook Faunal Studies. I.f One of 

 the specimens here illustrated is one of the types used by 

 White and Whitfield for their species Avicnlopecten 

 limaformis, and the other, the one showing the crenate hinge, 

 is the specimen used by Winchell as the type of his genus 

 Pernopecten. 



LlTHOPHAQA M1NUTA 11. Sp. 

 PL XV. f. 19. 



Shell minute, the type specimen having a length of 9^ 



* Trans. Acad. Sci. St. Louis. 10 : 84. 

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



