•j„ PALJEONTOLOGY OF NEW YORK'. 



Tliis specit's is distinjruislio.l hy its erect equiliiteral form, sub-equal ears, and 

 the fitronj;;, refjularly alternatinjr radii. 



Formation and locality. Intl..- upper beds of tlie Chemung group at Alleghany 

 Sulpliur Springs, Warren county, I'a. 



AVICULOPECTEN ItYS. 

 iM.ATi; VII, vm. i:t. 



Ariculo,Ktl.:, Itijx, Ham.. I'al. N. V.. vol. v, pt. 1. Pliiti^s .111. 1 KxphiiniticMis : PI. 7, tifr. 13. Jiin., 1SS3. 



SiiKi.i. small, broadly ovate, lengtli nearly equal to the height, slightly ol)li<iue ; 

 margins regularly romultd. nearly equilateral. 



Right valve depressed-convex. Left valve not known. 



Hinge-line straight, sub-central, having an extent of a little more than 

 one-half the greatest length of the siu'll. 



Beak acute, directed slightly forwai-il. Posterior >nnl)onal slope making a 

 "•reater an<de with the liin;j,c-line than tlie anterior, riiiho subtending a 

 right angle. 



Ears nearly e(iual. Anterior ear the larger, ol)tuse at the e.xtreiuity, 

 marked by several strong radii, separated from tlie innbonal region by a 

 strong sulcus. Posterior ear narrow, triangular, margin concave, separated 

 bv a distinct sinus IVom the body of the shell, with no rays of ornamenta- 

 tion ; olituse-angular. Hyssal sinus well-delined. 



Surface marked l)y sub-angular, rounded radii, which are regularly increa.sed 

 in size Avitli the growth of the slu'll, but rarely increased in number by 

 implantation; concentrically markc(| by line, regular, tlircad-likc stria' of 

 growth. 



Interior characters unknown. Hinge margin apparently simple. 



The specimen described has a length of 2o mm., height 27 mm., hinge- 

 line 1-5 mm. 



This .species is less oblicpie than .1. Idas, the hinge-line shorter, radii not 

 present <m the posterior ear, surlace markings coarser; and rays increasing 

 more rapiilly in size though fewer in nund)er. In A. cancellatus (==A. Halleanus, 



