lie, PALAEONTOLOGY OF NEW YORK. 



coiintv, is probalily IVoin the ILiiniltou slialcs at Fultonham ^ and the only 

 species from tliis locality, answering the description uiven, is A. Boi/dii. in 

 a condition in w liicli the i-adii and elevated concentric lamellae are more con- 

 spicnous than in an}' specimens from Cazonovia. Hamilton, or any other locality 

 in Central New York. 



Formation and localities. In the shales of the Hamilton i;rouj) ; aluuulant at 

 nnmerons ])laces in the eastern and central portions of the State. 



ACTINOPTERIA PEROBLIQUA. 



PLATK XIX, KKi. :il ; I'L.VTK I.XXXIV, FJG. H. 



AiHcida i>eriihru{ua, CoXK.\i). Jour. AcaJ. Nat. Sci., Pliila., vol. viii, p. 'I'ia, p\. 12, tig-. 1. 1S42. 

 Aclbuiptcria perubliqiia, (Conkad) Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 19, fig-. 31. 



Jan., 1883. 



SiiKLLof medinm size, suli-rhomhoidal ; body very oblique, narrow-ovate: leiiiith 

 one-third greater than the height ; anterior margin truncate or slightly con- 

 cave ; basal margin regularly arched and acutely roundcfl over the post-basal 

 side. 



Valves very convex. Left valve gijjbous in the upper part, angular along 

 the post-cardinal slope. Right valve somewhat less convex. 



Hinge-line straight, about two-thirds the length of the shell. 



Beak anterior, acute, prominent, inclineil forward. l^mbonal region 

 gibbous, subtending an acute angle. 



p]ar :i small lobe, defined by a distinct sulcus and shallow, elongate, byssal 

 sinus. Wing large, triangular, limited ly the angular post-cardinal slope 

 of the valves ; margin moderately concave, sloping forward ; extremity 

 anguliir. 



Test (as seen in the specimen, which is a partial east of the interior), 

 marked by irregular concentric striiv, which become fasciculate on the wing; 

 the surface apparently without rays. 



Muscular impression large, sub-quadrangular below the middle of the post- 

 cardinal slo[)e, from which, the pallial line cur\ing downward below the 



