Weller — Kinderhook Fanned Studies. 73 



plications varies from two to four in the sinus with always 

 one more on the fold. In addition to the plications both 

 valves are marked over their entire surface by fine radiating 

 striae which are often nearly obsolete in the casts. The 

 dimensions of an average specimen are: length, 22 mm., 

 breadth, 30 mm., thickness, 22 mm. 



Memarks. In 1855 Shumard * described Rhynchonella 

 missouriensis from the Chouteau limestone of Cooper and 

 Boone Counties, Missouri. In 1868 Meek and Worthenf 

 described a shell from Kinderhook, Pike County, Illinois, as 

 the same species, but in their remarks on the species they 

 pointed out that Shumard included what they considered to 

 be two distinct species in R. missouriensis. Their own speci- 

 mens they identified with the larger form of Shumard's 

 species and suggest the name striatocosiata for it, retaining 

 the original name missouriensis for Shumard's smaller form. 

 One of the most conspicuous features of Meek and Worthen's 

 R. sirialocostala are the fine radiating striae which cover the 

 entire surface of both valves in addition to the strong plica- 

 tions. Shumard mentioned no such markings in his descrip- 

 tion of R. missouriensis, but did mention fine, concentric lines 

 of growth, and in some specimens from the Chouteau lime- 

 stone at Sedalia, Missouri, believed to be R. missouriensis, 

 there are no signs of radiating striae but the fine concentric 

 lines of growth are finely shown. From a study of the speci- 

 mens, therefore, it seems that Meek and Worthen were mis- 

 taken in identifying their shell from Kinderhook, Illinois, 

 with Shumard's, whether the latter really includes two dis- 

 tinct species or only one. All of these shells were originally 

 described as members of the genus Rhynchonella, but they 

 are now referred to Pugnax. 



In the Kinderhook formations at Burlington, there are two 

 varieties or perhaps distinct species characterized by the fine 

 radiating striae of P. striatocostata . One of these occurs in 

 the limestone above the Chonopectus sandstone and may be 

 certainly identified with Meek and Worthen's shell from Kin- 



* I and II Rep. Geol. Mo. 204. 

 t Geol. Surv. 111. 3:450. 



