34 PALJEONTOLOGY OF NEW YORK. 



oviT till' cfiitri.' di' tlie valve, Ik'ioiiuii;; oliscun.- toward the margins. The 

 ears show the concentric stria» only. 



The characters of the interior are not known. 



A specimen of the lel't valvi' measures 'l■^ mm. in heitilit. H'.i mm. in Icniitii, 

 ami the hinjie-line "J! mm. 



This species in general expri'ssion resemhles A. tenuis, hut is distinct in its 

 smaller anterior ear, more obtuse heals, Drhicular I'orm, and more inx'gular and 

 stronger rays. Their geological positions ari' widely separated. 



Formation and locality. In soft shaly heds of the Corniferous limestone, which 

 constitute the upper portion of the group, at Lapham's mill, near A'ictor, 

 Ontario county, N. Y. 



AVICULOPECTEN INSIGNIS. 



I'I.\TK I, Kli; 8; IT.AIK UI, Klti 13; ami IT.ATK T.XXXI, VU. 7. 



AnU-iUiijM-HiH liuilgiivt. Hall. I';il. N. V.. vul. v. pt. 1. Plates jiiul Kxiilauatidii.s : PI. 1, tijf. S ; ]>l. S. lijr. 13. 



Jan.. 1SS3. 



Shell less than medium size, sub-rhomboidal, moderately ohlicpie, about one- 

 third longer than high; hasal margins rounde(l ; anterioi- and [xisti-rior mar- 

 gins obtusely angular or abruptly roundt-d, and I'xtending along the cardinal 

 slopes in a direct line to the lieak. 



IJoth valves are (piite convex; light valve somewhat the less convex. 



Hinge-line straight, nearly equal to the length of the shell. 



Beak obtuse-angular, prominent, directed forward, nearly central. Unibonal 

 regiiju ample, the sides subtending an obtuse angle, and sloping more 

 a})ruptly to the anterior than t<j the posterior margin. 



Ears sul)-eiinal, triangular. Anti-rior ear concave or Hat. ddiiicd hy a ilis- 

 tiiicl sulcus; margin dei'ply concave; extremitx' acuminati'. Hyssal sinus 

 ileep and well-markcfl. Posterior ear flattened, di'lined by the absence of 

 the stronger radii; extremity slightly acute; nuu'gin concave. 



Test thin, marked by strong radiating costa^, which in the left valve are 

 abruptly elevate<l and increase by interstitial addition ; crossed by infiecjueiit 



