174 PALAEONTOLOGY OF NEW YORK. 



MONOMERELLA GrEENII, sp. nOV. 

 Pr^ATE IV II, FIGS. 5 10. 



Shell elongate-subovate. Valves comparatively shallow ; shell-substance 

 relatively thin. Surfaces of contact very broad, especially toward the 

 posterior portion of the shell. Pedicle-valve with an erect but not hii:li 

 cardinal area, which is continuous with the broad margins. Umbonal cavi- 

 ties very short, rarely reaching to the liinge-line and sometimes scarcely more 

 developed tlian in Dinobolus. Cardinal slope well defined and divided by a 

 deep longitudinal groove. Cardinal buttress faint. Platform scarcely devel- 

 oped; the scars upon its surface usually faint, but the lateral impressions are 

 sometimes sharply defined. Crescent and terminal scars generally distinct. 

 Pallial sinuses usually discernible. Brachial valve Avith a low, rotund beak 

 and transversely striated area. Umbonal cavity deep. The deep groove of 

 the crescent is followed within by a sharply elevated ridge extending for the 

 entire length of the cardinal line ; terminal scars generally deeply impressed 

 and apparently compound. Platform represented only by a median thicken- 

 ing of the nniscular impressions, having the characteristic V^^h^psd outline 

 and sometimes divisible into the component scars. From the anterior ex- 

 tremity of this muscular area two diverging ridges pass toward the anterior 

 margin ; these may be connected with the pallial sinuses. 



This shell is readily distinguished from all other described species by the 

 general tendency toward suppression of the platforms and muscular scars, the 

 broad surface of contact, and the diverging anterior furrows of the brachial valve. 



From the dolomites of the Niagara group, between Cedarburgh and Grafton, 

 Wisconsin. 



Monomerella Kingi, sp. nov. 



PLATE IV II, FIGS. 1, 2. 



Shell subcircular or longitudinally oval. Pedicle-valve probably with a low 

 cardinal area, as far as may be judged l)y the size of the casts of the umbonal 

 cavities, which are quite short, mammilbrm, not extending to the canlinal 

 line. Cardinal buttress strong, produced as a septum nearly to the anterior 

 edge of the platform. Platform well developed, broadly V-^^^i'i'Psd ; anterior 

 wall vertical, not excavated; surface marked by strong impressions of mus- 



