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 surfiice similar to that occurring in the Swedish 

 Silurian species, 0. J^ovem, 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, IVtsconsm. 



Strophonella costatula, sp nov. 



PLATE LSXXIV, FIGS. 1.'). 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. Correspondmg 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- 



