BRACHIOPODA—PROTREMATA. 



241 



width of shell below. Pedicle valve projecting about one third its 

 length above the hinge line. Surface marked above by fine spines 

 and below by coarse, spine-bearing ridges. 

 Onondaga-Hamilton of New York, Nevada. 



139. P. spinulicosta Hall. (Fig. 293, c-d.) Devonic. 

 Differs from P. navicella in the broadly semielliptical or sub- 

 orbicular outline and in the beak of the pedicle valve which does 

 not extend beyond the hinge line as in P. navicella. 



Widely distributed in the Onondaga and Hamilton of North 

 America. 



140. P. subalata Hall. (Fig. 294, a.) Middle Devonic. 

 Semielliptical or semicircular, usually much wider than high. 



Distinguished by the irregularly scattered spines on the surface. 

 Illinois, Missouri, Minnesota. 



FlG. 294. a, Productella subalata ; b, c, P. hallana ; d, e, P. speciosa ; f, g, P. 

 arcuata ; h, P. pyxidata ; i, P. shumardana. (After Hall, except b, c, which are 

 after Walcott. ) 



141. P. hallana Walcott. (Fig. 294, b-c.) Upper Devonic. 



Semielliptical. Length and breadth nearly equal. Pedicle 

 valve very convex with umbo elevated above the hinge line. 

 Brachial valve deeply concave. Surface of pedicle valve marked 

 by fine radiating striae, a few strong growth lines and a few scat- 

 tered spines. Surface of brachial valve marked only by regular 

 concentric lines. 



New York, Iowa, Nevada, Northwest Territory. 



