342 PALEONTOLOGY OF NEW YORK. 



Surfiice covered with numerous very fine radiating striae. 



Length of the type specimen, 19 mm. ; width, 18 mm. ; depth, 9 mm. 



Hudson River group. East Tennessee. 



Orthis (Dalmanella) superstes, sp. nov. 



PLATE Vc, FIGS. 44-47. 



Shell of small size and having the general form and expression of O. hyhrida 

 Sowerby. Hinge-line short, beaks but slightly elevated. Marginal outline 

 varying from siibquadrate to subcircular. Valves about equally convex. In 

 the pedicle-valve the beak is somewhat inflated and slopes evenly in all 

 directions for nearly one-half of the shell ; from this point onward is a broad, 

 low median sinus, which is most conspicuously developed in old and gibbous 

 shells. In rare instances there is a low elevation in the bottom of this sinus 

 The opposite valve also bears a median sinus which takes its origin at the 

 beak. In the interior of the pedicle-valve the muscular area is sharply de- 

 fined, subquadrate in outline, the adductor scars small and the diductors well 

 developed. In the brachial valve the cardinal process and crural plates are 

 prominent ; the muscular area well defined and quadruplicate. 



The external surface of the valves is covered with fine, elevated strife, of 

 which twenty of the coarsest reach the beak ; this number increasing by 

 intercalation to about fifty at the margin. Near the margin very fine 

 concentric striae are visible. 



Length of a normal individual, 12 mm.; width, 13 mm.; depth, 9 mm. 



Chemung group. Near Howard, Steuben county, N. Y. 

 Orthis (Rhipidomella) Oweni, sp. nov. 



PLATE VI, FIGS. 19-21. 



Shell having somewhat the outline of O. Vanuxemi, but more elongate trans- 

 versely and gently sinuate or emarginate on the anterior edge. The shells 

 are usually flattened, but where the form is retained the pedicle-valve shows 

 a hinge-line whose length is somewhat less than one-half the transverse 



