LAMELLIBRANCHIATA. 517 



24 mm. in height at the beaks, and 27 mm. in height near the posterior 

 extremity. The various phases of this species seem to be all due to the 

 degree and direction of pressure during the process of imbedding. 



Formation and localities. In the Oneonta sandstone, at Mt. Upton, Chenango 

 county ; Gilbertsville, Otsego county ; on the road from Jefferson to Gilboa, 

 and at the base of the hills to the south of Jefferson, Schoharie county, N. Y. 

 Prof. J. J. Stevenson has found a single valve of this fossil in the Catskill red 

 sandstone on Wills creek, about one mile from Hyndman, and 1,600 feet above 

 the base of the formation, in Bedford county, Pennsylvania. (Report T. 2, p. 103.) 



This species is the only mollusk known in the Oneonta sandstone. At Mt. 

 Upton it occurs in a shaly stratum associated with numerous plant remains. 

 The bed containing the specimens of this species in great abundance is sur- 

 mounted by at least five hundred feet of shales, altern<ating with bands of 

 gray and reddish sandstones, containing great numbers of plant remains which 

 have not been identified. 



The relations of the Oneonta sandstone to the Hamilton and Chemung 

 groups has heretofore been discussed,* and all subsequent studies of the locali- 

 ties in Delaware, Otsego and Chenango counties sustain the views published by 

 me in 1870 and 1880. This deposit, consisting of red and gray compact or 

 shaly sandstones, red and green marls, etc., comes in at about the close of the 

 Hamilton period, or more properly may be regarded as the result of changes 

 which terminated the conditions of the Hamilton group. The changes super- 

 vening in the east, at that time, seem to have affected the succeeding strata 

 throughout the entire length of the State, although this particular portion of 

 the series apparently merges into the succeeding Portage group, of which, farther 

 west, it forms a part. The presence of numerous fragmentary and drifted land 

 plants indicates the proximity of land, and in Schoharie county, just below 

 the commencement of the red deposits, we find the trunks of two species of 

 Psaronius, stsmding erect in the place and position in which they have grown, 

 enveloped by an argillaceous sandstone with their bases resting upon and imbed- 



* 8«e Report upon the State Museum for 1870, and a paper i-ead before the National Aca<lemy of Sciences 

 in New York, 1880, of which an abstract was published in "Science," December 11, 1880. 



66 



