39 PALiEONTOLOOY OF NEW-YORK. 



diflTers in being more ovate, as well as in the form and division of the muscular 

 scar, and more depressed posterior side*. 



Geological formation and locality. In Schoharie grit : at Clarksville and Knox, 

 Albany count}-, N.Y. 



Pliolidops liaiiiiltoiiia;. 



PLATE III. 

 Pkolidopt kamiltoniir : Hail, Thirteenth Report on the State Cabinet. 1860, p, 92. 



Shell regularly and uniformly ovate, broader near the posterior end : 

 apex excentric, little elevated, and slightly inclining to the posterior 

 side. 



Substance of the shell thin, and flattened towards the margins. Surface 

 marked by fine closely arranged lamellose striae. Interior smooth, 

 except an ovate, somewhat auriculate, and sometimes slightly bilobed 

 prominence beneath the apex, which marks the muscular impression. 

 The casts of the interior show a comparatively large muscular impres- 

 sion, which is shield-shaped or subovate and somewhat auriculate, or 

 with a deeper impression on each side above the middle. In one (dorsal?) 

 valve, the impression is a little bilobed near the lower end ; and in 

 another, which appears to be the ventral valve, there is a faint radiating 

 or digitate impression on the lower half of the muscular scar. The 

 surface, when magnified, shows indications of minute interrupted ra- 

 diating striae. 

 This species is the smallest of any described ; having a length of fourteen- 



liundredths of an inch, with a width of twelve-hundredths in the widest part. 



It is not rare, but we find only separated valves. 



The observations upon this genus, under the generic description, will shoAV 



the facts regarding the known species, and their geological range (See Introduc- 

 tion to this volume). 



Geological formation and locality. In the shales of the Hamilton group at Darien 



in Erie county, at Moscow in Livingston county, and other places in Western 



New- York. 



* For a dctcriptlon of the Oriskany sandstone species, P. arenariui, gee Addenda to this volume. 



