62 BEACHIOPODS. 



outward that a few of them run out on the cardinal edge be- 

 fore reaching the lateral margins; striae of the ventral valve 

 nearly always increasing by bifurcation ( some of them divid- 

 ing two or three times ), while that on the dorsal valve gen- 

 erally increases by the intercalation of shorter ones between 

 the longer. A few distant sub-imbricating marks of growth 

 are sometimes seen toward the front and lateral margins ; 

 while on perfectly preserved specimens the radiating striae 

 may sometimes be seen to be roughened by minute elevated 

 concentric lines, that are more or less interrupted in crossing 

 some of the striae. 



Horizon and localities Lower Silurian, Hudson shales : 

 Warren and Jefferson counties. 



Orthis subcarinata HALL. 



Orthis subcarinata Hall, 1857 : Reg. Rep. Univ. New York, p. 43. 



Orthis subcarinata Hall, 1859: Pal. New York, vol. Ill, p. 169, pi. xii, 



figs. 7-21. 

 Orthis subcarinata Meek & Worthen, 1868: Geol. Sur. Illinois, vol. Ill, 



p. 373, pi. vii, figs. 6a-d. 



A rather small subovate form resembling 0. elegantula. 

 Horizon and localities. Upper Silurian limestone : Gyrene 

 ( Pike county ), Bailey landing ( Perry county ). 



Orthis iowensis HALL. 



Plate xxxviii, figs. 6a-c. 



Orthis iowensis Hall, 1858 : Geology Iowa, vol. I, p. 488, pi. ii, figs. 4a-i. 

 Orthis iowensis White, 1881 : Geol. Sur. Indiana, 10th Ann. Rept., p. 501, 

 pi. v, figs. 10-12. 



Shell transversely ovoid; hinge-line short, about one-half 

 the width of the valves. Ventral valve much deeper than the 

 dorsal, with a broad median fold ; beak prominent, area small. 

 Dorsal valve flattened, with a broad shallow sinus. Surface 

 marked by fine radiating lines. 



Horizon and localities. Devonian, Hamilton limestone: 

 " Grand Tower " ( Perry county ). 



