FOSSILS OP THE HUDSON RIVEE GROUP. 101 



and flattened, measuring about four and a half inches in length, by a 

 breadth, in its flattened condition, of three and a quarter inches across 

 the middle of the outer chamber. The specimen preserves the filling of 

 seven chambers, and is imperfect below, several having been removed. 

 The occurrence of a species of this genus in rocks of this age is a matter 

 of considerable interest. The only other known in this county, so far as 

 we are aware, is the G. obesum, Bill., described in the Geological Report 

 of Canada for 1857 ; but as we have not been able to compare it with a 

 description of that species, we do not know how nearly this one may re- 

 semble it. 



Formation and locality : In the upper part of the shales of the Hudson River group, 

 near Dayton, Ohio. Ohio State collection. Collected by Prof. Edward Orton. 



ENTOMOSTBACA. 



Genus LEPERDITIA. 



Sub- GENUS ISOCHILUSTA. 



Leperditia (Isochilina) cylindrica. 



Plate 4, fig. 5. 



Leperditia {Isochilina) cylindrica, Hall ; Descr. New Species of Fossils from the Hud- 

 son River Group, etc., p. 7. 

 Leperditia (Isochilina) cylindrica. Hall ; 24th Rept. State Cab., p. 231, pi. 8, fig. 12. 



The original description of this and the following species of bivalve 

 entomostracans is copied from the above cited reports, as we have not 

 seen any additional specimens, and the originals have been returned to- 

 their owners ; consequently no new facts have been collected in relation 

 to their characters or habits. 



"Carapace minute, seldom exceeding two-hundredths of an inch in 

 length, nearly twice as long as wide ,• valves very convex and cylindrical, 

 the anterior and posterior ends sub-equal and strongly rounded; car- 

 dinal line much shorter than the length of the valve ; tubercle obsolete." 

 Surface smooth. 



There appears to be no tubercle or prominence of any kind on the sur- 

 face of this minute species, and so far as can be ascertained the valves do 

 not overlap on the basal border ; but as they have not been seen in con- 

 nection, this feature on so small a species may easily be overlooked. 



Formation and locality: In the Hudson River group, at Cincinnati. The original 

 specimens were from the collection of Mr. C. B. Dyer. 



