352 PALEOZOIC PALEONTOLOGY. 
the other by almost imperceptible variations. In New Jersey the 
Oriskany specimens are more elongate than the Helderbergian #. 
singularis, the inflection of the cardinal border of the pedicle valve 
is more conspicuous and the strong median stria is much less con- 
spicuous, and sometimes may not be recognized at all. The denticula- 
tion of the lateral margins of the two valves is absent from the Hel- 
derbergian specimens, but this is not a conspicuous feature of the 
Oriskany specimens, and may apparently be absent altogether in 
some cases. 
BEACIIIA SUESSANA (Hall). 
Plate XLVII., Figs. 5-14. 
1859. Rensseleria suessana Hall, Pal. N. Y., vol. III., p. 459, pl. 107, 
figs. 1-15. 
Description.—Shell longitudinally subovate or sub-elliptical in out- 
line, usually longer than wide; hinge-line shorter than the greatest 
width. Pedicle valve moderately convex, most elevated along the 
median line posterior to the middle, sometimes more or less flattened 
laterally; the lateral margins in adult shells sometimes abruptly in- 
flected ; beak sharply pointed, incurved, but not touching the opposite 
valve, perforated at the apex by a small, circular foramen; delthyrium 
closed by deltidial plates above and by the cardinal process of the 
brachial valve below; cardinal margin abruptly inflected, forming a 
false cardinal area. Brachial valve a little less convex than the pedicle, 
point of greatest elevation posterior to the middle; cardinal margin 
nearly straight or sloping gently from the slightly-produced beak; the 
cardinal angles obtusely rounded, lateral margins sometimes abruptly 
inflected in adult shells. Surface marked by indistinct, radiating 
plications and by concentric lines of growth. 
The dimensions of a complete specimen are: length, 30 mm.; width, 
26 mm.; thickness, 14 mm. Another large individual has a width of 
42 mm. 
Remarks.—This species, originally described from the Oriskany of 
Cumberland, Maryland, is not an uncommon form in the New Jersey 
fauna. Very few of the New Jersey specimens retain the radiating 
markings, but the concentric markings are often stronger and more 
numerous than is usally the case in the Maryland specimens. These 
