No. 109. 1 161 



Spirifer arata (n. s.). 



Pal. N.Y. Vol.iv. 



Cast of interior transversely oval or oblong, gibbous ; valves 

 nearly equal ; hinge nearly or quite equalling the greatest width, 

 rectangular at the extremities ; front broadly sinuate in the 

 middle : dorsal valve convex, rising gradually into an indistinct 

 mesial fold, which is marked along the middle by a profound 

 sulcus from near the beak to the front ; beak incurved : ventral 

 valve very convex at the umbo ; mesial sinus broad subangular, 

 not strongly defined at the margins, extending from, the beak to 

 the front, where it terminates in a broad rounded projection ; 

 beak elevated ( '? ) ; area high, sloping from the beak to the ex- 

 tremities, slightly arcuate and inclined back beyond the hinge; 

 foramen large, having the form of an equilateral triangle ; la- 

 teral slopes of the valves marked by about fifteen flattened or 

 depressed plications, which are separated by small linear de- 

 pressions. A few strong imbricating wrinkles of growth mark 

 the valves near the margins. 



This species bears some general resemblance to S. gramdifera, but is 

 smaller than that species usually occurs, is less elevated in front with a 

 proportionally broader sinus, and is well marked by the strong groove 

 down the mesial fold : the plications are also more flattened, and separated 

 by linear grooves. These characters, with others, seem quite sufficient to 

 distinguish the species, even in the form of casts. 



This species corresponds in some respects with Spirife?- ( Dellkyris ) 

 duplicata, Conrad ( Jour. Acad. Nat. Sci. Phila., Vol. viii, pa. 261, pi. 

 14, f. 16 ) ; but the superior valve is more gibbous or ventricose, and the 

 ribs are not angulated. Since no allusion is made to the ventral valve or 

 area, it is probable that Mr. Conrad described his species from a single 

 valve. 



Geological position and locality. In the shales of the Hamilton group, 

 Otsego county. 



[ Sen. No. 109.] 11 



