DESCRIPTIONS OF NEW SPECIES 
FIGURED IN VOLUME VIII, PART II. 
OrTHIS ? QLYPTA, Sp. nOV. 
PLATE LXXXIV, PIGS. 8, 9. 
Shell small, transverse, with long, straight hinge, making the greatest diam¬ 
eter of the shell, short along the median axis ; marginal outline transversely 
subelliptical Pedicle-valve with a broad and low median sinus and generally 
depressed surface The exterior bears from twelve to sixteen low, flat plica¬ 
tions, separated by narrow sulci, and sometimes with a fine groove on the sur¬ 
face of each, These extend from apex to margins, and are crossed by fine, 
undulating, subconcentric lines apparently in two oblique sets, producing a 
peculiarly reticulated or wavy surface similar to that occurring in the Swedish 
Silurian species, 0. Jiioveni, Lindstrom The muscular area of the pedicle valve 
is small. Length of an average pedicle-valve, 12 mm.; width, 18 mm. 
Niagara dolomites. Near Milwaukee, Wisconsin. 
Strophonella costatula, sp. nov. 
PLATE LXXXIV, PIGS. 15, 16. 
Shell subsemicircular in outline ; hinge-line straight or slightly arched ; sur¬ 
face depressed concavo-convex. 
Pedicle-valve elevated at the beak, becoming rapidly depressed anteriorly, 
the median depression continued upon the short linguiform extension at the 
anterior margin. Corresponding to this depression is a broad anterior fold on 
the opposite valve. The surface of both valves is covered with a few coarse, 
round, sharply elevated ribs, which rapidly bifurcate or multiply by implanta- 
