342 
PALAEONTOLOGY OF NEW YORK. 
Surface covered with numerous very fine radiating strige. 
Length of the type specimen, 19 mm.; width, 18 mm. ; depth, 9 mm. 
Hudson River group. East Tennessee. 
Okthis (Dalmanella) superstes, sp. nov. 
PLATE VC, FIGS. 44-47. 
Shell of small size and having the general form and expression of O. hybrida 
Sowerby. Hinge-line short, beaks but slightly elevated. Marginal outline 
varying from subquadrate 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 striae, 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 0. 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 
