376 Systematic Paleontology 



strire, of which there are from four to five on each plication and one or 

 two in each depression. The strife are best developed in the postero- 

 lateral regions and diminish in strength toward the fold and sinus. The 

 dorsal fold has from six to seven plications and the sinus six. The total 

 number of plications on each valve varies from twenty-four to forty. 



Length 4 cm. ; width 4.5 cm. 



Very young individuals are like E. iclntfieldi and have been confounded 

 with it. However, the undefined fold and sinus and the fine radial lines 

 will distinguish it. The great number of plications, the fine striae, and 

 the undefined fold and sinus readily separate E. sinuata from E. medialis. 

 However, when specimens have less than thirty plications they strongly 

 resemble E. medialis, but are more elongate and the fold and sinus have 

 more plications. 



Occurrence. — Oriskany Formation, Eidgely Member. Knobly 

 Mountain near Cumberland, Collier's Eun, 21st Bridge. 



Collections. — -Maryland Geological Survey, U. S. National Museum. 



Eatonia hartleyi n. sp. 

 Plate LXVI, Figs. 2, 3 



Description. — The specimens of this species are suggestive of E. 

 sinuatd, but are distinguished in having not only a deeper or more convex 

 ventral valve and more plications, but especially in having from eight to 

 eleven plications in the fold and sinus along the anterior margin, while 

 in E. sinuata there are from four to seven. This difference is due to the 

 fact that in E. hartleyi several plications are bifurcated shortly before the 

 animal has attained half its growth. The total number of plications on a 

 valve in the latter species varies between thirty-four and thirty-seven 

 against twenty-six and thirty-four in E. sinuata. Externally this new- 

 species is not strongly suggestive of Eatonia, but more of Plethorhyncha, 

 but as the interior muscular area is that of the former genus it is best 

 referred to it. 



Length 3 cm.; width 3.5 cm. 



Occurrence. — Ortskany Formation, Eidgely Member. Martin 

 Mountain, Allegany County. 



Collection. — Yale University (Hartley Collection). 



