Orthis. 



534 



HcM.TP^^ 



Orthus subcarinata, Hall. Pal. N. Y. Vol. 3, 1859, p. pL 



12, fig, 

 18, dor- 

 sal in- 

 terior; 



19 a, 



V e ntral 



interior; 



JM 20^,dor- 



^^ sal cast ; 



21, ven- 



^*kralcast. 



Lower Helderherg. Recognized by Dr. Barrett in the Storm- 

 ville shale or upper division of the Lower Helderberg forma- 

 tion about Port Jervis. G6, p. 132. — VL 



Orthis subcircula. New species, Simpson, Trans. Amer. 

 Yd ^.^-w . ^^ o Philosophical Soc. 1889, Vol. 



page — fig. founded on specimens 

 501-30, 41, 42. (00 Oat.) in Hale 

 and Hall's collections ; also 877-1, 

 878-1, 882-2, 6, got at the McKee's 

 ore bank in Mifflin Co., Pa. Also at 

 Orbisonia ore banks in Huntingdon Co., Pa. — Clinton^ Va, 



Shell broadly oval, nearly circular; height usually about 

 three-fourths the width ; greatest width just below the middle ; 

 cardinal line short, length less than half the width of the shell ; 

 extremities curving outward, the lateral marginc abruptly 

 rounded, and the basal margins broadly rounded ; on the ven- 

 tral valve slightly constricted at the middle. Dorsal valve 

 flattened, greatest convexity a little below the beak, 2:ently 

 sloping to the front and lower lateral margins, more abruptly 

 curving to the cardinal extremities; at the middle of the base 

 a shallow depression, which continues aboutone-half of the dis. 

 tance to the beak. Ventral valve more convex, greatest con- 

 vexity about one-third the length from the beak; beak incurved 

 and projecting beyond the area line. 



Surface marked by conspicuous radiating strias, which are 

 sometimes of uniform size, but usually near the base there are 

 very fine alternating striae. The large stria3 are marked at in- 



A.P.S. 



.Tr..{889.\ 



