BRACHIOPODA—NEOTREMATA. 201 



XIV. Iphidea Billings. 



Pedicle valve subconical, strongly elevated at beak; flattened 

 posteriorly, forming an appearance resembling a true cardinal 

 area; this area is crossed by a broad triangular ridge (deltidium). 

 Hinge line nearly straight. Beak excentric, perforated by the 

 pedicle opening. Brachial valve semicircular, slightly convex. 

 Surface of shell covered with fine concentric striae. The posses- 

 sion of the large convex deltidium distinguishes it from Acrotreta. 

 Cambric. 



39. I. bella Billings (Fig. 234, h.) Lower Cambric. 

 Small and conical. Pedicle valve about y 2 inch wide by slightly 



less long. Surface covered with fine concentric striae which are 

 continued across the large flat area. These striae are crossed by 

 a few obscure radiating ones. 



Massachusetts, Quebec, Labrador. 



40. I. pannulus (White). Lower and Middle Cambric. 

 Differs from /. bella in its smaller size ( )/% inch) and in the charac- 

 ter of the surface markings ; these consist of a fine network of ob- 

 lique, raised lines, visible under a lens. 



New York, Utah, Nevada, Quebec, British Columbia. 



41. I. swantonensis Walcott. (Fig. 234, i-j.) Lower Cambric. 

 Hemispheric to semioval outline with high hinge area, marking 



the greatest width of the shell and surface marked by concentric 

 growth lines. (This is also known under the name Paterina labra- 

 do fie a.) 



Georgian of Swanton and Highgate Springs, Vermont. 



XV. Trematis Sharpe. 



Subcircular. Pedicle valve unevenly convex, depressed in pos- 

 terior portion. The margin of the pedicle valve is interrupted by 

 the pedicle fissure which extends almost to the subcentral apex ; 

 internally the sides of this fissure are often thickened. Brachial 

 valve convex; apex marginal or slightly projecting. In interior of 

 pedicle valve radiating sinuses extend from the apex. Surface of 

 both valves covered with punctures which are arranged either in 

 quincunxial order or in radiating rows and penetrate the outer cal- 

 careous layers of the shell, but not the inner corneous ones. Or- 

 dovicic. 



