10 



Orthisina festinata. (N. sp.) 



Fig. 11. 



Fig. 12. 



Fig. 13 



Pig. u.—Ventral vsdve and side view of 0. festinata. Fig. 12.— Area of ventral 

 valve. Fig. 13. — Camerella antiquata. 



Description. — >Subquadrate or semioval, hinge-line equal to the greatest 

 width of the shell. Ventral valve sub-pyramidal, beak elevated, surface 

 with a straight or slightly convex slope in all directions to the margin, 

 area triangular, a little inclined backwards, foramen about as wide as 

 high, closed by a convex deltidium which is perforated at the beak. 

 Dorsal valve nearly flat. Surface with angular bifurcating ribs, five or 

 sLx in the width of two lines at the margin, crossed by fine concentric 

 striae, of which there are from seven to ten in one line. 



Width on hinge-linge from 10 to 15 lines ; length about a third less 

 than the width. Height of beak of ventral valve from two to three lines. 



Both valves show longitudinal undulations radiating from the beak to 

 the margin. 



This species closely resembles some of the ordinary forms of the genus, 

 but differs internally from any known to me in the Second Fauna in the 

 absence of the dental plates, no traces of which can be perceived in the 

 casts. 



Locality and Formation. — IJ mile east of Swanton in Vermont. 

 Potsdam group. 



Collcdors.—Dv. G. M. Hall, and Rev. J. B. Perry. 



Camerella antiquata. (N. sp.) 



Fig. 13. 



Description. — Ovate or subcircular, beaks obtusely pointed (as seen in 

 the cast), both valves moderately or rather strongly convex. Surface 

 with from 8 to 10 small rounded ribs which do not reach quite to the 

 beaks. 



