250 Mr. T. R. Joaes on North American 



one of which (anterior) is smaller than the other. Coarsely 

 sculptured with broad shallow pits. One specimen, showing 

 the two valves united, and of a light-brown colour, occurred 

 with the many other Entomostraca in the small specimen of 

 limestone from Pauquette's Rapids. 



[From the United States.) 



1. Leperditia alta, Conrad, sp. PL X. figs. 10, 11. 



Annals Nat. Hist. 2 ser. vol. xvii. p. 88. pi. 7. figs. 6 & 7. 



Numerous individuals of this species occur in the dark- 

 coloured " Tentaculite-limestone^'* of Schoharie, accompanied 

 by Spirifer plicatus. The specimens are mostly in an indif- 

 ferent state of preservation ; but here and there evidences of the 

 smooth surface of the valves are obtained. In outline most of 

 them resemble fig. 7a of PI. 7 above referred to ; but others are 

 more tapering anteriorly, as in the figures now given (PI. X. 

 figs. 10 & 11). 



I have now no doubt that the Arctic specimens before described 

 belong to this species. 



The '^ Tentaculite-limestone " of Schoharie belongs to the 

 Lower Helderberg group of strata, — the " Premeridian " group 

 of the classification adopted by the Professors Rogers. 



2. Leperditia gihbera, Jones, Annals Nat. Hist. 2 ser. vol. xvii. 

 p. 90. pi. 7. figs. 8-10. 



Var. scalaris. PI. X. figs. 7-9. 



In the grey " Waterlime-rock^' of AVilliamsville, specimens of 

 which, collected by Sir C. Lyell, are now in the Geological 

 Society's Museum, are some casts of a fine Leperditia (one spe- 

 cimen being \ inch long and -^^ inch broad, with others smaller 

 and of different sizes) which has the general aspect oi L. gibhera 

 of the Silurian limestone of Beechey Island, but is larger and 

 less convex, and has a much smaller hump on the dorsal region 

 of the left valve. 



In the black limestone (weathering grey) of the " Scalent 

 group" (Rogers), — of about the same age as the " Waterlime" 

 of Williamsville, — there also occur specimens of a similar form. 

 These are in a beautiful state of preservation, exhibiting glossy 

 black valves. The left valve bears a distinct, but small, dorsal 



* In the collection of Silurian fossils brought by Sir C. Lj-cll from North 

 America, and now in the Museum of the Geological Society of London, 

 are several specimens of this Leperditla-limestone. 



