BRACHIOPODA. 353 



lobed by a more or less conspicuous median furrow. Brachial valve strongly 

 concave. 



Surface smooth, with a few inconspicuous concentric growth-lines, and 

 faint radiating striae on the inner lamellae toward the margins. 



Lower Helderberg group (Shaly limestone). Near Clarksville, N. Y. 

 Chonostrophia Helderbergia, sp. nov. 



PLATE XVb. fig. 14. 



Shell tenuous, semi-elliptical in outline. Hinge-line straight and making the 

 greatest diameter of the valves. Valves nearly flat, the pedicle-valve being 

 gently concave and the brachial correspondingly convex. Cardinal areas 

 very narrow; marginal spines not observed. Teeth of the pedicle-valve 

 well developed on either side of the moderately broad delthyrium ; 

 at their bases arises a median septum, strongest at the point of beginning 

 and continuing for one-half the length of the valve. In the brachial valve 

 the crural plates are very short, subparallel to the hinge-line and apparently 

 coalesced with the short cardinal process. No traces of muscular scars re- 

 tained. 



Surface covered with a great number of exceedingly fine, subequal radiating 

 striae, all of which are apparent on the interior of the shell, even to the 

 bases of the teeth and crural plates. 



Lower Helderberg group (Shaly limestone). Albany county, N. Y. 

 Strophalosia Rockfordensis, sp. nov. 



PLATE XVIU, riGS. 1-3. 



Shell semielliptical in outline, somewhat elongate. Hinge-line scarcely as 

 long as the greatest diameter of the valves. Cardinal area well developed 

 on each valve, that of a pedicle-valve bearing a convex deltidium; scar 

 of attachment on the pedicle-valve covering only the apical region. Sur- 

 face regularly convex, depressed toward the cardinal angles ; bearing scat- 



